The present invention relates to an abnormal switching monitoring device and method. A time point when a high-side switch in which a first electrode receives an input voltage is turned on, a time point when a low-side switch that is connected to a second electrode of the high-side switch is turned on, a time point when a charge current begins to flow to a bootstrap circuit, and a time point when a charge current stops flowing to the bootstrap circuit are compared so as to determine whether or not non-zero voltage switching occurs. The bootstrap circuit supplies an operating current to a gate driver controlling a switching operation of the high-side switch.