Laser light detection circuit

A laser light detection circuit comprising:

• a light receiving element receiving laser light and generating a current corresponding to intensity of the received laser light;
• a current voltage conversion circuit converting the current generated by the light receiving element to a voltage signal and outputting the voltage signal;
• an amplifier amplifying the voltage signal outputted by the current voltage conversion circuit and outputting the amplified voltage signal;
• a first constant-current source supplying an operation current to the amplifier;
• a first transistor having a base to which the voltage signal amplified by the amplifier is applied;
• a second constant-current source connected to an emitter of the first transistor;
• a second transistor having a base connected to the emitter of the first transistor;
• a bypass transistor connected between the emitter of the first transistor and the ground;
• and
• a control circuit controlling the first and second constant-current sources and the bypass transistor so as to form a bypass current route from the second constant-current source to the ground through the bypass transistor by starting the operations of the first and second constant-current sources and turning on the bypass transistor for a predetermined period when the circuit starts operating.