A standby power supply apparatus is provided in which a supply voltage of the standby power source, supplied before electronic apparatuses such as TVs or video players are switched on, is reduced by half to sharply reduce the consumption of the standby electric power. According to the standby power supply apparatus, it is possible to reduce by half the electric power loss due to switching the standby power converter controlling the standby electric power of the power supply apparatus on and off. Additionally, the standby electric power can be sharply reduced without an additional increase in manufacturing costs of the power supply apparatus.