Abstract: A synchronized flash emission of a strobe for high speed successive photo shooting. A transistor and a first resistor are connected in parallel to a resistor second of a strobe interface circuit. A control circuit switches the transistor ON for a duty cycle of 1/10 to increase the current flowing through a Triac to be greater than a holding current. The increased current raises the voltage of a synchronized signal to HIGH when the Triac is switched OFF. The strobe detects a HIGH to LOW transition of the synchronized signal even for successive photo shootings at high speed so that synchronized successive flashes can be provided.