Saisen is money offered to the gods (Shinto), Buddha and so on. It mainly refers to money which is thrown in Saisenbako (offertory boxes) placed in front of shrines or temples.
After throwing money in Saisenbako, visitors clap their hands at shrines (Shinto) or put their palms together at temples, and then they pray for their wishes or offer their thanks to Shinto and Buddhist deities in their minds while closing their eyes. Although the amount of Saisen is not fixed, many people throw in coins as Saisen.
It is often the case that they make a pun combining their wishes and the amount of Saisen. A recent example is "shiju-goen"(four 10-yen coins and a 5-yen coin which come to forty five (shiju go) yen) which means forming a lot of good relationships.
In hatsumode (the practice of visiting a shrine or temple at the beginning of the New Year), many self-employed people throw in as Saisen "fuku-koi"(2,951yen) which means bringing good luck. Sometimes, worshipers place Saisen before Jizo Bosatsu (Jizo Bodhisattva statues) or shintai (an object of worship housed in a Shinto shrine and believed to contain the spirit of a deity) even without Saisenbako.
Because some worshipers also place Saisen in front of lists of Buddhist images or sculptures of deities exhibited in museums, there may be written instructions "Don't place Saisen."
In praying to Shinto and Buddhist deities, mostly the five main cereals wrapped in paper have been dedicated since ancient times. But with the development of the money economy, more coins than rice and millet are placed on the altars of shrines or temples. Therefore, Saisenbako accepting coins were generated spontaneously.
According to "The Diary of Kaigen-sozu" written by a Buddhist monk in the Muromachi period, a "sansenbitsu" box was set up at Tsurugaoka-hachimangu Shrine in 1540. This is thought to be the oldest document about Saisenbako in Japan.
It is said that the visit to the Ise-jingu Shrine and the pilgrimage to the head temple became popular among the common people in the Muromachi period, and that the custom of offering Saisen was then established.
Many Saisenbako have the form of rectangular boxes. Under their ladder-like lids, two sloping boards face each other at the lowest point so that money on the bottom will not be touched.
Most Saisenbako are made of wood. In temples and shrines where many people make a "hatsumode" visit, supersized Saisenbako are set up only during the New Year's period. Recently, damage to Saisenbako has occasionally occurred, for example, being forcibly broken open or being taken away entirely. Saisenbako made from metal are also used to avoid such damage. One of the standard souvenirs of excursions in Japan is a Saisenbako-shaped money box which is sold at many tourist spots.