According to one embodiment, a detection device comprises a base, a sensor layer, a collimator, a plurality of lenses, and a spacer. The sensor layer is placed on the base and includes a plurality of sensors which output detection signals corresponding to incident light. The collimator layer is placed on the sensor layer and includes a collimator having a plurality of openings which overlap the sensors, respectively. The plurality of lenses are placed on the collimator layer and overlap the openings, respectively. The spacer protrudes more than the lenses in a stacking direction of the base, the sensor layer and the collimator layer.