A fixing unit includes an endless belt accommodating a heat source inside a loop formed by the endless belt, a rotary pressing member rotating in contact with the endless belt in a pressure contact section, and a heat transfer member secured to a side plate within the loop of the endless belt to support and heat the endless belt with heat conducted from the heat source. The heat transfer member has an opening opposite the rotary pressing member. A securing member is disposed in the opening of the heat transfer member in pressure contact with the rotary pressing member via the endless belt. The heat transfer member and the securing member collectively include a pair of latching parts to firmly connect the heat transfer member and the securing member with each other when one of the latching parts is fitted to the other one of the latching parts.