An image forming apparatus is provided with an image forming station and a fixing unit including a heating member. The fixing unit includes a coil for generating a magnetic field for induction heating the heating member; a first core arranged to face the heating member with the coil located therebetween; a bar-shaped second core including a cut-off portion and arranged in a magnetic path between the first core and the heating member, when seen in a magnetic field generation direction by the coil, to form the magnetic path together with the first core; and a magnetic adjusting mechanism for changing the posture of the second core between a first posture for guiding a magnetic field by retracting the cut-off portion from the magnetic path and a second posture for increasing magnetic resistance by locating the cut-off portion in the magnetic path by rotating the second core about an axis thereof.