To remove disturbance while measurement being carried out and measure the distance to an object existing nearby by condensing laser beams reflected by the object, converting it into an electric signal, and applying the voltage to a photomultiplier while boosting it.

A pulse laser oscillator 12 oscillates pulsed laser beam 1 at several ns based on trigger signals from a trigger signal generating apparatus 11. A condenser 13 converges pulsed laser beams 1a reflected by an object 101 and sends to a photomultiplier 14. The photomultiplier 14 receives the pulsed laser beam 1a from the condenser 13 and converts it into an electric signal and transmits it to a computing processing apparatus 16 and at the same time the light reception sensitivity fluctuates due to pulsed voltage from a pulsed high voltage power source 15. The high voltage power source 15 applies gradually increasing pulsed voltage to the photomultiplier 14 based on the trigger signals from the trigger signal generating apparatus 11. The computing processing apparatus 16 computes the distance to the object 101 based on the time of reception of the trigger signals from the generating apparatus 11 and the time of reception of the electric signals from the photomultiplier 14.