An LED driving circuit can improve characteristics. A first current increasing circuit 10i4 is constituted of a first slow regulating unit 10i41 and a post-stage first supplying circuit 10i43 and, from a point in time of output switching of a first comparator 10i2, that is, when a set temperature exceeding a reference potential Va is attained, gradually increases a temperature compensated current IT1 (ΔI1) and thereby suppresses the lowering of emission output. Here, by gradually increasing the temperature compensated current IT1 by making use of charging/discharging functions of a capacitor, etc., that is, by increasing the temperature compensated current IT1 over a longer time than a pulse width that a photodetecting element, onto which light from an LED 11 is made incident, can respond within, pulse width distortion and jitter can be suppressed.