A device and method for detecting a zero crossing and voltage amplitude of a commercial power source voltage inputted to an electronic device, from a single pulse signal are disclosed. The apparatus for detecting a zero crossing and a voltage amplitude from a single pulse signal includes: a first calculation unit that compares the commercial power source voltage to a first reference voltage to determine whether or not the commercial power source voltage is smaller than the first reference voltage; a second calculation unit that compares the commercial power source voltage to a second reference voltage smaller than the first reference voltage to determine whether or not the commercial power source voltage is larger than the second reference voltage; a pulse output unit that outputs a pulse if the commercial power source voltage is smaller than the first reference voltage but larger than the second reference voltage; and a detecting unit that detects a zero crossing and a voltage amplitude by analyzing the pulse which has been outputted from the pulse output unit.