It is an object of the invention to, in fault detection of a PWM load device, provide a fault detection device and a fault detection method, which are capable of appropriately detecting fault of the load device in the case where such load device is connected the duty ratio of the PWM waveform of which is different, or where such load device is connected the magnitude of current of which is different. The fault detection device samples a current flowing through the load device on a predetermined cycle, decides, based on sampled values, a current-driven period and decides, by using sampled values in the current-driven period, a drive current value for determining whether or not there is a fault.