A power saving apparatus of a monitor which is capable of reducing power consumption in a monitor by controlling the power supplied to a signal sensor in a power saving mode and a controlling method thereof are provided. The power saving apparatus includes a power supply unit which supplies operational power to the signal sensor, which senses an input state of a video synchronization signal input into thereto and generates data based on the input. A microprocessor determines whether the monitor is in a power saving mode or a normal mode based on the data generated by the signal sensor, and then cuts off the power supplied to the signal sensor if the monitor is determined to be in a power saving mode. The power is intermittently resupplied to and cut off from the signal sensor during the power saving mode.