A luminometer apparatus includes, inside a light-shielded room, a container rack loaded with holding containers, a dispensation mechanism that dispenses a liquid, a rotary plate that turns, while holding a plurality of reaction containers which accommodate a mixture liquid of a sample and a luminescent reagent on a concentric annular plate, and is provided with a gap allowing the container rack to pass therethrough between at least a pair of adjacent ones of the reaction containers, and a photodetection unit that performs luminescence measurements. The light-shielded room has an insertion opening having a width allowing for insertion of the container rack and provided to be openable and closable. The rotary plate is provided with a region in which the container rack can be installed inside a region of passage of the reaction containers, when turning, and is provided to be turnable where the light-shielded room is in a closed state.