A light source apparatus and a light source driving circuit are provided. The light source driving circuit includes an operation amplifier (OP-AMP), a transistor, and a switch unit. A first input terminal and an output terminal of the OP-AMP couple to a predetermined voltage and a control terminal of the transistor, respectively. A first terminal of the transistor couples to a light source. The switch unit includes a first signal terminal receiving a first voltage greater than a predetermined voltage, a second signal terminal coupled to a second input terminal of the OP-AMP, a third signal terminal coupled to a second terminal of the transistor, and an enabling terminal receiving a driving voltage. A voltage of the third signal terminal or a voltage of the first signal terminal is determined to transmit to the second signal terminal in accordance with the driving voltage.