Disclosed are abnormality detecting apparatus and method for a high-voltage circuit (A), in which: a square wave pulse is outputted to a measuring point (p1) with a switch (SW1) set off, the switch (SW1) provided between an inverter circuit (2) and the ground, a difference voltage (Vp-p) between a voltage (Vh) detected at a phase of T/2 and a voltage (V1) detected at a phase of T is obtained, the occurrence of a ground fault is detected based on the size of the difference voltage (Vp-p); and the square wave pulse is outputted to the measuring point (p1) with the switch (SW1) set on, and it is judged that a loosening of a fastening section (p2) occurs when the difference voltage (Vp-p) exceeds a reference voltage (Vref2).