An inverter circuit (20) includes a transformer (T2) including a primary winding and a secondary winding including a high voltage terminal, a first copper foil (P21), a power stage circuit (21) electrically connected to the primary winding, a detection circuit (22) including a second copper foil (P22) and an impedance (Z2), a protection circuit (23) outputting a protection signal, and a pulse width modulation controller (24) controlling output of the power stage circuit according to the protection signal. The second copper foil and the first copper foil are separated. An equivalent capacitor is formed between the second copper foil and the first copper foil, detecting voltage output from the high voltage terminal. The impedance is electrically connected between the second copper foil and ground, dividing a voltage detected by the equivalent capacitor.