In DC/DC converter circuit, the peak value of the reactor current is found based on output voltage and an input voltage, thereby, the operation with the predetermined electric current mode is thereby enabled. The AC/DC converter circuit is run with a predetermined current mode, the power factor improvement is accomplished. The first control part 211 inputs a detected value of output voltage Eo, and a turn-off timing predicted value of switch Tr of the DC/DC converter 1 is calculated. The first control part 211 sends the calculation result to the switch drive signal generate part 213. The second control part 212 inputs the detected value of the output voltage and the input voltage, and it receives the turn-off timing predicted value from the first control part 211. Even more particularly, the second control part 212 calculates the peak value of the reactor current of the DC/DC converter 1 based on the turn-off timing predicted value, and it calculates the time that the reactor current decreases to a predetermined preset value from the peak value as a turn-on timing predicted value.