Light source device and concentration measuring device

The light source device (2) has an LED (21) and the following parts. The constant current drive circuit (101) supplies a constant current to the LED (21). The current correction circuit (102) transmits a portion of the constant current supplied from the constant current drive circuit (101) as a bypass current to the bypass circuit (124), supplies the remaining current as an LED current to the LED (21), and corrects such that, when the LED current is smaller than a predetermined target current value, the bypass current is reduced, and the LED current is reduced. When the LED current is greater than a predetermined target current value, the bypass current is increased. 光源装置(2)具有LED(21)以及以下的各部分。恒电流驱动电路(101)朝向LED(21)供给恒电流。电流校正电路(102)将从恒电流驱动电路(101)供给的恒电流的一部分作为旁路电流送至旁路电路(124)，将剩余的电流作为LED电流供给至LED(21)，并以如下方式进行校正：在LED电流相对于规定的目标电流值小的情况下，减少旁路电流，在LED电流相对于规定的目标电流值大的情况下，增加旁路电流。