An induction hardening monitoring apparatus (20) comprising: a current sensor (21) for detecting output current from a high-frequency inverter (11); a voltage sensor for detecting a voltage generated in a heating coil (14) connected between output terminals of the high-frequency inverters (11) together with a capacitor (12) in an equivalent circuit manner; and a controller (23) for monitoring a hardening processing based on a detection signal from the current sensor (21) and a detection signal from a voltage sensor (22), wherein the controller (23) monitors a hardening processing by calculating an effective value of output current from the high-frequency inverter (11) based on a detection signal from the current sensor (21) and calculating an effective value of voltage generated in a heating coil (14) based on a detection signal from the voltage sensor (22); or further calculating load impedance based on each effective value.