The present invention can control the power of an output from a device, which changes the amplitude of an input and outputs a result of the change, according to the frequency of the input so that the power is close to a desired value. An output control system (1) includes an amplitude changer (2) which controls the ratio of a change in amplitude according to a control signal, a discrete attenuator (14) which outputs an output signal obtained by attenuating an output from the amplitude changer while discretely setting an amount of the attenuation, a measurement result changer (18) which changes a measurement result of the output signal, a set voltage recording unit (24) which records a correspondence between a value of the control signal and a value of the output signal when the input signal is at a predetermined frequency, a measurement result correcting unit (44) which corrects an output from the measurement result changer (18) according to the frequency of the input signal, a target value correcting unit (42) which corrects a target value of the output signal according to the frequency of the input signal, a voltage setting unit (26) which sets the value of the control signal, an attenuation setting unit (12) which sets the amount of the attenuation according to the frequency of the input signal and a change setting unit (13) which sets an amount of the change provided by the measurement result changer (18).