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.