There is provided an optical amplifier, which includes: an optical amplification medium; a pump light generator configured to generate pump light with a power corresponding to a set control value and supply the generated pump light to the optical amplification medium; a first controller including a level control circuit configured to generate the control value such that an output power of the optical amplification medium approaches a target power, and a limiter configured to limit a range of the control value in variable; and a latch circuit configured to set a specific control value to the pump light generator during a period in which the first controller is in a stop state.