The switching of LLC converter becomes hard switching at the time of overload. In this study, we elucidated the mechanism of hard switching and the current path. The reason of hard switching is the commutation of magnetizing current to the secondary side. It is possible to make a judgement whether overload or not from the voltage value at the end of resonance. Voltage value can be obtained from the circuit constants. In this way, it becomes possible to judge the success or failure of soft switching from the circuit constants.