An integrator of a vehicular radar system has multiple switches and
multiple capacitors, which are connected with the switches, for each one
of photoreceptive elements. The integrator integrates light reception
signals, which are output from the photoreceptive elements, by switching
the switches to a connected state one after another in a predetermined
order at a predetermined time interval until a predetermined time passes
after every emission of the laser light and by switching the switches to
the connected state one after another in a predetermined order at a
predetermined time interval if the laser light is emitted predetermined
times. Thus, the integrator can integrate the light reception signals,
which are output from the multiple photoreceptive elements, in parallel.