In a passenger detection apparatus for a vehicle, a microcomputer conducts
a timer counting operation using a sub-clock signal fed from an CR
oscillation circuit in a stand-by state and carries out a zero-point
correction on a load sensor in an activated state. In addition, the
microcomputer calibrates the accuracy of the timer count through the use
of a main clock signal fed from a crystal oscillator. This enables the
timer count to be conducted in a low current dissipation state by the CR
oscillation circuit, and enables the accuracy of the timer count to be
surely maintained through the calibration based on the main clock signal.