An apparatus for protecting an occupant in a vehicle includes a pair of image sensors for taking images of an area on a seat in the vehicle. Transverse-direction shifts between corresponding portions of the images are calculated. Longitudinal-direction positions of objects whose images are in the portions of the images taken by the image sensors are measured in response to the calculated transverse-direction shifts. A longitudinal-direction position of an occupant on the seat is decided in response to the measured longitudinal-direction positions of the objects. Occupant protecting operation at a time of occurrence of a collision of the vehicle is changed in response to the decided longitudinal-direction position of the occupant. From the measured longitudinal-direction positions of the objects, one corresponding to a highest position with respect to the vehicle and being in front of the seat is selected as a longitudinal-direction position of a head of the occupant.