To provide an automatic gain control circuit, capable of shortening its adjustment and testing time and reducing its production cost to reduce the number of circuit components.

The automatic gain control circuit is used for a radio communication system, with which a reception signal received by a radio part is transmitted to a control part by way of an optical transmission path, and in the gain control circuit, the gain of the gain variable circuit for variably controlling the level of the reception signal and compressing it to a level, equivalent to the dynamic range of the optical transmission path, is controlled based on the level of a pilot signal which is outputted from the control part.