A fixing device comprising: a rotatable member for conveying a recording material for carrying an image; a back-up member (32, 33) for forming a fixing nip, together with said rotatable member, in which the image is to be fixed on the recording material; a pressure-applying mechanism (36, 37) for applying pressure to the fixing nip; a cam for releasing the pressure applied to the fixing nip by acting on said pressure-applying mechanism (36, 37); a motor, capable of rotating normally and reversely, for driving said cam; a first power transmitting path (45, 46; 245, 46, 38) for permitting transmission of power of said motor; a second power transmitting path (47, 48; 47, 205, 206, 207) for permitting transmission of the power of said motor; a swingable gear for transmitting the power of said motor to said first power transmitting path (45, 46; 245, 46, 38) or said second power transmitting path (47, 48; 47, 205, 206, 207); a swingable arm for holding said swingable gear; and a preventing member for preventing movement of said swingable arm by being engaged with said swingable arm, wherein of said first power transmitting path (45, 46; 245, 46, 38) and said second power transmitting path (47, 48; 47, 205, 206, 207), at least said first power transmitting path (45, 46; 245, 46, 38) is a path for permitting transmission of the power of said motor to said cam, and wherein when said motor rotates in one direction, said swingable arm is tilted so that said swingable gear is moved to a first position for permitting transmission of the power of said motor to said first power transmitting path (45, 46; 245, 46, 38), and when said motor rotates in the other direction, said swingable arm is tilted so that said swingable gear is moved to a second position for permitting transmission of the power of said motor to said second power transmitting path (47, 48; 47, 205, 206, 207), characterized in that said preventing member is movable, and when said swingable gear is located at the first position, said preventing member engages with said swingable arm so that said swingable gear is prevented from moving from the first position, and when said swingable gear is located at the second position, said preventing member is spaced from said swingable arm. a rotatable member for conveying a recording material for carrying an image; a back-up member (32, 33) for forming a fixing nip, together with said rotatable member, in which the image is to be fixed on the recording material; a pressure-applying mechanism (36, 37) for applying pressure to the fixing nip; a cam for releasing the pressure applied to the fixing nip by acting on said pressure-applying mechanism (36, 37); a motor, capable of rotating normally and reversely, for driving said cam; a first power transmitting path (45, 46; 245, 46, 38) for permitting transmission of power of said motor; a second power transmitting path (47, 48; 47, 205, 206, 207) for permitting transmission of the power of said motor; a swingable gear for transmitting the power of said motor to said first power transmitting path (45, 46; 245, 46, 38) or said second power transmitting path (47, 48; 47, 205, 206, 207); a swingable arm for holding said swingable gear; and a preventing member for preventing movement of said swingable arm by being engaged with said swingable arm, wherein of said first power transmitting path (45, 46; 245, 46, 38) and said second power transmitting path (47, 48; 47, 205, 206, 207), at least said first power transmitting path (45, 46; 245, 46, 38) is a path for permitting transmission of the power of said motor to said cam, and wherein when said motor rotates in one direction, said swingable arm is tilted so that said swingable gear is moved to a first position for permitting transmission of the power of said motor to said first power transmitting path (45, 46; 245, 46, 38), and when said motor rotates in the other direction, said swingable arm is tilted so that said swingable gear is moved to a second position for permitting transmission of the power of said motor to said second power transmitting path (47, 48; 47, 205, 206, 207), characterized in that said preventing member is movable, and when said swingable gear is located at the first position, said preventing member engages with said swingable arm so that said swingable gear is prevented from moving from the first position, and when said swingable gear is located at the second position, said preventing member is spaced from said swingable arm.