A gate drive device drives a gate of a semiconductor switching element constituting an upper or lower arm of a half bridge circuit which supplies an output current, which is alternating current, to a load. The gate drive device detects a peak value of an element voltage which is a voltage of a main terminal of the semiconductor switching element or a change rate of the element voltage when the semiconductor switching element is switching. The gate drive device acquires a maximum value among a plurality of peak values or a plurality of change rates during a predetermined detection period including a period in which the semiconductor switching element performs switching multiple number of times.