The light source device includes at least one excitation light source which emits primary light, a light conversion member which emits secondary light that contains the primary light and wavelength-converted light obtained by converting a wavelength of at least part of the primary light, a sensor which detects the primary light and the wavelength-converted light, and a controller which obtains a first signal which is a signal indicating the detected primary light and a second signal indicating the wavelength-converted light detected by the sensor. The controller determines an operation safety parameter based on a ratio of an output value of the first signal to an output value of the second signal, and controls the at least one excitation light source based on the operation safety parameter with respect to a predetermined threshold or an amount of change of the operation safety parameter from that during normal operation.