A light source apparatus is provided which includes semiconductor laser elements that emit laser light according to an inputted current signal, a light receiving element that receives the laser light emitted from the semiconductor laser elements, and a controller that controls light emission of the semiconductor laser elements. The controller includes a first semiconductor laser element drive circuit that outputs a current signal to the semiconductor laser elements according to an instruction signal, a second semiconductor laser element drive circuit that adjusts the current signal based on a light quantity of the laser light received by the light receiving element, and outputs the adjusted current signal to the semiconductor laser elements, and a circuit switching section that switches between the first and the second semiconductor laser element drive circuits according to an instruction signal.