A light source driving apparatus including a voltage converting unit, a switching unit, a feedback unit and a control unit is provided. The voltage converting unit provides a driving current to drive a light source module. The switching unit is controlled to be conducted or not by a switch signal. The feedback unit detects a load status of the light source module, and provides a feedback signal accordingly. The control unit modulates pulse widths of the switch signal according to the feedback signal, a signal upper limitation, and a signal lower limitation, so as to control the switching unit to be conducted. The voltage converting unit includes an energy storage element. When the switching unit is conducted, the energy storage element stores a part of energy provided by the input power source. When the switching unit is not conducted, the energy storage element provides the driving current.