The invention relates to an automatic response/light measurement device and a method therefor, and the purpose is to effectively and quickly perform an optical measurement relating to a reaction with high reliability without increasing a device size. The device is configured to have: a container group in which a plurality of reaction containers are arranged; a measurement mount provided with a plurality of coupling ends that are joinable with apertures of the reaction containers, and have light guide portions that optically connect with the interior of the joined reaction containers; a mount transfer mechanism; a measuring device having a measuring end having at least one light guide portion that is optically connectable to the light guide portions of the coupling ends, that is able to receive light based on an optical state within the reaction containers; an on-mount measuring end transfer mechanism; and a measurement control portion.