To correct a variance in accuracy of initial light quantity measurement for a light quantity measuring photo diode while suppressing an increase in production cost.

The LED light source is provided with an LED 12, a variable constant current driver 13, a photo diode 14 to detect the quantity of light of the LED 12, a memory 101 wherein a value obtained by directing a reference light to the photo diode 14 is stored as a reference light corresponding value or respective current control values of the LED 12 corresponding to output values obtained from the photo diode 14 are stored in advance, and a control unit 102. When the control unit 102 is activated, it reads the current control values corresponding to the output values given from the photo diode 14 from the memory 101, corrects them on the basis of the reference light corresponding values, and calculates current control correction value. During operation after activation, the current control correction value is given to the variable constant current driver 13 as a variable constant current value, to control a value of current flowing in the LED 12 to be equal to the current control correction value.