A plasma generator capable of adjusting the amount of plasma generation in a simple configuration includes a control circuit controlling a frequency of an AC power supplied to a piezoelectric transformer and a control signal generation circuit providing a control signal to the control circuit. The plasma generator is configured so that the control signal output from the control signal generation circuit is appropriately adjusted. The control circuit controls the frequency of the AC power so as to bring a target value, which is set based on the control signal provided from the control signal generation circuit.