The present invention relates to an error information detection circuit and an error feedback circuit, which detect the error of an output voltage from a voltage induced to a winding. The circuit for detecting error information of an output voltage of a transformer from voltage induced to the feedback winding of the transformer and feeding back the error information includes a flyback period detection circuit (34) for detecting a flyback period from a voltage induced to the feedback winding. A comparison unit (35) compares the induced voltage of the feedback winding with a reference voltage and outputs a result of comparison. A logic unit (36) outputs error information of an output voltage of the transformer according to a flyback period detection output of the flyback period detection circuit and the output of the comparison unit. An up/down control unit (32) outputs a feedback value corresponding to the error information.