An optical sensor (1) for appropriately updating a crosstalk value is provided with: a photocount type first light receiving unit (5) for receiving target object reflected light (L1) and cover panel reflected light (L2); and a determining circuit (6) which, on the basis of a first light reception pulse signal (SPAD_SG1) based on at least one of the target object reflected light (L1) and the coverpanel reflected light (L2), and on the basis of a reference pulse signal (TX), determines whether or not the object reflected light (L1) has been received by the first light receiving unit (5).