A control circuit for DC-DC converters and a control method therefor wherein unstable operation in which output voltage fluctuates can be detected and the unstable operation be prevented from continuing are provided. The control circuit includes: an error amplifier ERA1 that has an inverting input terminal to which detecting voltage V1 detected according to output voltage is inputted and a non-inverting input terminal to which reference voltage e1 is inputted, and amplifies the difference voltage of detecting voltage relative to reference voltage e1; and a detection unit 50 that detects that an error output signal VOP of the error amplifier ERA1 stays at a predetermined voltage level. The detection unit 50 includes: a signal determination unit that determines that the predetermined voltage level is out of a normal operating range; and a duration count unit that detects that the predetermined voltage level stays out of the normal operating range for a predetermined time by the signal determination unit.