Hoan-den was the premises where portraits of the emperor and empress (called "goshin-ei portrait") and the Imperial Rescript on Education were housed before and during the war. As goshin-ei portraits were themselves granted as Imperial gifts from the Taisho period to the Showa period, it is estimated that Hoan-den came into existence in those periods (construction of Hoan-den in the elementary schools became active in around 1935). Moreover, one of the reasons for setting the system of night duty at schools was to protect the goshin-ei portrait.
In the four major festivals, all school staff and students were obliged to make a deep bow and read the Imperial Rescript on Education with respect. Moreover, they had to make a deep bow after straightening their clothes not only when they arrived at school and left school, but also whenever they passed in front of the portraits.
At first, Hoan-sho (place for displaying the goshin-ei portraits and the Imperial Rescript on Education, the predecessor of Hoan-den) was established at the auditorium or inside the staff room or principal's office. However, in the Hoan-sho, there was a high possibility that the goshin-ei portrait would be exposed to danger, if the schoolhouse collapsed due to fires or earthquakes. Indeed, some heroic tales of principles who died protecting the goshin-ei portrait in the Great Kanto Earthquake, air raids and fires have been passed on.
Therefore, aiming at a more perfect system, Hoan-sho established inside the schoolhouse was reformed to a strongbox style. Furthermore, the separated premises of 'Hoan-den' were constructed. The former premises incorporated into the schoolhouse was frequently observed in junior high schools under the old system of education, while the latter premises constructed separately was frequently observed in elementary schools.
Observed as architecture, Hoan-den had various variations. Many of them were elaborately designed, ranging from the Hellenized architecture, the ferro-concrete buildings and the Western-style architecture built of brick to the conventional Shinto shrine-style architecture and others. Hoan-den provides observers with a glimpse of the great efforts to attain a fire-proof and earthquake-proof structure with matchless strength despite its small size, as well as a design with solemnity and gravity so as not to damage dignity. Moreover, the competition concerning the architectural design of Hoan-den was held in 1933.
However, such strong small buildings had a drawback of 'Moisture easily fills the building.'
Schools were often forced to submit a letter of apology after they carelessly made a stain on the goshin-ei portrait.
Hoan-den was abolished because of the Shinto Directive (direction for the separation of government and religion) issued by the General Headquarters of the Allied Powers (GHQ) on December 15, 1945. After the war, many of the Hoan-den were dismantled or buried in the ground, but not all goshin-ei portraits were returned to the emperor. Hoan-den that escaped being dismantled still remain even now although the number is small, used as a warehouse or converted to a Shinto shrine or an ossuary, taking advantage of its solemn external appearance. The Hoan-den established by the former Misato Jinjo higher elementary school is registered on "cultural properties" as 'war remains,' although it was partially destructed. Some Hoan-ko (storeroom for displaying the goshin-ei portrait and the Imperial Rescript on Education, the predecessor of Hoan-den) remain within the schoolhouses where the school preserves old schoolhouses or auditoriums that were built in the prewar period.
Hoan-den were established either within the schoolhouse or outside the schoolhouse separately. In either case, it was a rule to establish Hoan-den at a pure location near the principal's offices, staff room, night watchman's room and so on. Inside measurements were requested to be larger than 85 cm in depth, 1.5 meters in height, 1.2 meters in width. As for the structure, Hoan-den needed to be built from ferro-concrete, have walls 25 cm or thicker, and a complete safe-typed and dual-structured door with either a single swing door or double-leaf doors. In addition to the fire-proof and earthquake-proof structure, Hoan-den were requested to be equipped with heat-resistant and damp-proof structures by using asbestos for the inside and outside, as well as by laying boards made from empress tree or hinoki cypress inside. Furthermore, it was regulated that the height of the shelf on which goshin-ei portrait was enshrined was about 50 cm.