To provide a delay adjustment circuit whose size and costs are reduced by changing into an integrated circuit, an optical receiver, and an optical transmission system.

A delay adjustment section 31 has inductances L1, L2 connected between respective load resistors R1, R2 of differential FET1, FET2 and a resistor R3 for bias adjustment each, and FET3, FET4 connected to the inductors L1, L2 in parallel each. A control signal is applied to each gate terminal of the FET3, FET4. In a general differential circuit, when the inductor is connected between the load resistor in the differential FET and a GND, characteristics in a group delay are changed by the inductance components of the inductor, thus adjusting the group delay at a frequency coinciding with an inputted electric signal by utilizing the characteristics for controlling the inductance component of the inductors L1, L2.