A light source device comprising: at least one light source which can output light at a plurality of output levels; a light monitor unit that detects emitted light emitted from the light source; a light source drive unit that controls a drive current or an applied voltage of the light source such that a detection value detected by the light monitor unit indicates a predetermined target value; a warning unit that performs a primary warning when the drive current or the applied voltage of the light source reaches a predetermined reference value, and performs a predetermined process on a basis of a deterioration level of the light source after the primary warning is performed, wherein the deterioration level of the light source is a value set in accordance with a degree of decrease in a maximum light amount actually emitted with respect to an initial value of the maximum light amount, wherein the warning unit prohibits driving of the light source beyond a predetermined output, as the predetermined process, by causing the target value to be reduced, wherein the light source drive unit drives the light source such that the detection value detected by the light monitor unit comes to match the target value corresponding to a target output level selected from among the plurality of output levels, and the warning unit causes the target output level to decrease in stages; characterised in that the light source device further comprises: a learning unit that learns the detection values detected by the light monitor unit in a case where illumination light is caused to be output at each of the output levels when the light source device is first driven. at least one light source which can output light at a plurality of output levels; a light monitor unit that detects emitted light emitted from the light source; a light source drive unit that controls a drive current or an applied voltage of the light source such that a detection value detected by the light monitor unit indicates a predetermined target value; a warning unit that performs a primary warning when the drive current or the applied voltage of the light source reaches a predetermined reference value, and performs a predetermined process on a basis of a deterioration level of the light source after the primary warning is performed, wherein the deterioration level of the light source is a value set in accordance with a degree of decrease in a maximum light amount actually emitted with respect to an initial value of the maximum light amount, wherein the warning unit prohibits driving of the light source beyond a predetermined output, as the predetermined process, by causing the target value to be reduced, wherein the light source drive unit drives the light source such that the detection value detected by the light monitor unit comes to match the target value corresponding to a target output level selected from among the plurality of output levels, and the warning unit causes the target output level to decrease in stages; characterised in that the light source device further comprises: a learning unit that learns the detection values detected by the light monitor unit in a case where illumination light is caused to be output at each of the output levels when the light source device is first driven.