Jyodoji-Jyododo is one of the religious architectures that express the nobility of the Land of Happiness making use of daylight. The mechanism how the daylight reaches a statue of Amitabha-Tathagata in Jyodoji-Jyododo, it has peculiar luminous environment that no other historic architectures have, has not proved yet. Then, for the purpose of proving the mechanism of daylight that influence a statue of Amitabha-Tathagata, we conducted following 3 simulations; 1) Inter-reflection simulation with Jyodoji-Jyododo architectural model and simplified Amitabha-Tathagata model to obtain distribution of illuminance. 2) Specular reflection simulation for identifying the parts of the architecture which principally contribute to glitter of the statue. 3) Simulation of changing the angle of ceiling to make clear the relationship of the phenomenon and the architecture. From the results, we found that the daylight from the back of a statue of Amitabha-Tathagata repeats diffuse reflection, and a statue of Amitabha-Tathagata is shined by the daylight gathered at the ceiling. And the reason of a steeply slanting roof is infered that the daylight is took in a statue of Amitabha-Tathagata.