An optical receiver, comprising: - a photodetector adapted for converting a light reception signal into a current signal; - a preamplifier adapted for converting the current signal output from the photodetector into a voltage signal; - gain control means adapted for detecting an average voltage of the voltage signal output from the preamplifier by a first average voltage detection section that has a first time constant or a second average voltage detection section that has a second time constant longer than the first time constant, and for controlling, with use of the detected average voltage, a conversion gain of the preamplifier to be a desired gain according to a reception level of the light reception signal; characterized by a convergence determination means adapted for determining whether the gain control means is in a transient state or in a steady state, and for generating a time constant switching signal for selecting the first average voltage detection section of the gain control means when it is determined that the gain control means is in the transient state and for selecting the second average voltage detection section of the gain control means when it is determined that the gain control means is in the steady state, wherein the convergence determination means comprises: - a third average voltage detection section that has a third time constant longer than the first time constant of the first average voltage detection section and shorter than the second time constant of the second average voltage detection section, for detecting an average voltage of the voltage signal output from the preamplifier; - a difference voltage detection section adapted for calculating a difference voltage between the average voltage detected by the first average voltage detection section and the average voltage detected by the third average voltage detection section when the first average voltage detection section is selected; and - a comparator section adapted for comparing the difference voltage with a predetermined threshold voltage and determining whether the gain control means is in the transient state or in the steady state based on a result of the comparison. - a photodetector adapted for converting a light reception signal into a current signal; - a preamplifier adapted for converting the current signal output from the photodetector into a voltage signal; - gain control means adapted for detecting an average voltage of the voltage signal output from the preamplifier by a first average voltage detection section that has a first time constant or a second average voltage detection section that has a second time constant longer than the first time constant, and for controlling, with use of the detected average voltage, a conversion gain of the preamplifier to be a desired gain according to a reception level of the light reception signal; - a third average voltage detection section that has a third time constant longer than the first time constant of the first average voltage detection section and shorter than the second time constant of the second average voltage detection section, for detecting an average voltage of the voltage signal output from the preamplifier; - a difference voltage detection section adapted for calculating a difference voltage between the average voltage detected by the first average voltage detection section and the average voltage detected by the third average voltage detection section when the first average voltage detection section is selected; and - a comparator section adapted for comparing the difference voltage with a predetermined threshold voltage and determining whether the gain control means is in the transient state or in the steady state based on a result of the comparison.