Patent ID: 8190036

Claim:
An optical signal receiving apparatus, comprising: a variable optical attenuation controller, disposed in a former stage of an optical signal receiving unit and executes attenuation control of signal level of input optical signal to the apparatus by a variable attenuation having an upper limit of a predetermined maximum attenuation; and an attenuation controller that includes a first PNP transistor, an emitter earth type current source connected with an emitter of the first PNP transistor, and a capacitor arranged between a base of the first PNP transistor and earth and a resistor arranged between the base of the first PNP transistor and a positive electrode power source, the attenuation controller controlling the variable optical attenuation controller so that the variable attenuation is the maximum attenuation at a time of turning on the power of the apparatus or at a time of recovery from input optical signal break of the apparatus.