An optical receiver including: a preamplifier capable of changing a conversion gain in accordance with a reception level of a received burst signal; a gain control circuit capable of switching between a fast time constant and a slow time constant; and a convergence determination circuit for outputting a time constant switching signal in accordance with a state of the gain control circuit (transient state or steady state) and a reset signal between the burst signals. This configuration can switch the time constant of the gain control circuit at an appropriate timing.