To provide a stroboscope slave unit for making the light quantity of strobe light for assisting the strobe light from a digital camera main body from its outside finely variable.

A photodetecting sensor 1 and a differentiation circuit 2 detect the first strobe light emitted from the inside of the camera main body, to issue a light emission detecting signal. A light emitting circuit 3 issues a light emission driving signal for emitting the second strobe light for assisting the strobe light from the outside of the camera main body, in accordance with a light emission detecting signal from the differentiation circuit 2. A light quantity control photodetector 6 and a light quantity control circuit 7 detect the light quantity value of the reflected light of the second strobe light, when it is reflected by an object and compares the light quantity value with a reference value consecutively changed according to the setting of variable resistance VR1 to send out a light quantity control signal for controlling the light quantity of the second strobe light to the light emitting circuit 3.