To provide a current supply source which produces a current value having a large change rate to temperature or having an increased change rate to temperature, when the temperature exceeds a threshold value, and also to provide a semiconductor laser drive circuit which has less fluctuation in its optical output power over a wide range of temperatures.

A laser driving current supply source 4 for driving a semiconductor laser 1 includes two voltage-controlled current supply sources 41 and 42 and a control voltage generation source 43. The voltage generation source 43 outputs control voltages to the two voltage-controlled current supply sources 41 and 42, in such a manner that the current source linearly changes its current value to a temperature to turn off the current source 42 when the temperature is lower than a threshold value, and to linearly change the current value when the temperature is higher than the threshold. As a result, temperature characteristics of the semiconductor laser can be compensated for in a wide range of temperatures, and thus there can be realized a semiconductor laser drive circuit which can produce a less-fluctuated optical output power.