To provide a ranging device capable of detecting the erroneous operation of a signal processing IC by forcibly finishing ranging routine when the voltage value of an integrating capacitor is out of a previously set range in the ranging routine.

In this device, range-finding is performed by projecting luminous flux toward a ranging object plural times, receiving the reflected light of the luminous flux projected to the ranging object and successively integrating an output signal in accordance with a distance to the range-finding object. The voltage value of the integrating capacitor 6 in the ranging routine is detected (S18 and S28), and the range-finding routine is forcibly finished when the voltage value of the capacitor 6 is out of the previously set range.