An object is to provide a reaction detecting device in which a height dimension of the device itself can be set to be small to realize space saving, unevenness of measurement sensitivity for each reaction container is minimized, and high-sensitivity and high-precision reaction detecting is possible, the device includes: a reflective plate disposed above a temperature controllable reaction block disposed in a reaction chamber constituted in a main body to reflect light; and a light source lamp and a camera arranged in the main body, the light from the light source lamp is reflected by the reflective plate to enter each reaction container from above, and light such as fluorescence directed upwards from a reaction specimen is reflected by the reflective plate to enter the camera. |