A reaction force generating apparatus comprising: a rotation member which is rotated by a load; a motor which applies a reaction force in a direction opposite to a rotation direction of the rotation member to the rotation member; a rotation shaft which is rotatably installed in a transmission passage through which a reaction force generated by the motor is transmitted to the rotation member; a first gear which is rotatably attached to the rotation shaft; a second gear which is disposed on a downstream side of the transmission passage from the first gear, and coupled to the first gear; a transmission member which is rotatably installed in the transmission passage, and to which the second gear and the rotation member are attached; and an one-way clutch which is interposed between the rotation shaft and the first gear in the transmission passage, wherein the one-way clutch has: a state in which, when a load is applied to the rotation member to rotate the first gear in a first direction, the one-way clutch connects the transmission passage to the rotation member; and a state in which, when the load applied to the rotation member is released from the rotation member to rotate the first gear in a second direction, the one-way clutch blocks the transmission passage,: a deceleration mechanism for decelerating a rotation to be transmitted to the rotation member from the motor; a motor case in which the motor is accommodated; a gear case which is fixed to a front face of the motor case; and a control board which controls the motor, wherein the deceleration mechanism is an one-stage deceleration mechanism having: the first gear serving as an input gear; and the second gear serving as an output gear, characterized by: the second gear is a sector gear, the control board is disposed in front of the motor and above the deceleration mechanism, and is covered with a circuit board cover, and the motor case, the gear case, the rotation member and the control board are disposed within a range of an axial dimension of the rotation shaft in the direction along the rotation shaft. a rotation member which is rotated by a load; a motor which applies a reaction force in a direction opposite to a rotation direction of the rotation member to the rotation member; a rotation shaft which is rotatably installed in a transmission passage through which a reaction force generated by the motor is transmitted to the rotation member; a first gear which is rotatably attached to the rotation shaft; a second gear which is disposed on a downstream side of the transmission passage from the first gear, and coupled to the first gear; a transmission member which is rotatably installed in the transmission passage, and to which the second gear and the rotation member are attached; and an one-way clutch which is interposed between the rotation shaft and the first gear in the transmission passage, wherein the one-way clutch has: a state in which, when a load is applied to the rotation member to rotate the first gear in a first direction, the one-way clutch connects the transmission passage to the rotation member; and a state in which, when the load applied to the rotation member is released from the rotation member to rotate the first gear in a second direction, the one-way clutch blocks the transmission passage,: a deceleration mechanism for decelerating a rotation to be transmitted to the rotation member from the motor; a motor case in which the motor is accommodated; a gear case which is fixed to a front face of the motor case; and a control board which controls the motor, wherein a state in which, when a load is applied to the rotation member to rotate the first gear in a first direction, the one-way clutch connects the transmission passage to the rotation member; and a state in which, when the load applied to the rotation member is released from the rotation member to rotate the first gear in a second direction, the one-way clutch blocks the transmission passage,: a deceleration mechanism for decelerating a rotation to be transmitted to the rotation member from the motor; a motor case in which the motor is accommodated; a gear case which is fixed to a front face of the motor case; and a control board which controls the motor, wherein a deceleration mechanism for decelerating a rotation to be transmitted to the rotation member from the motor; a motor case in which the motor is accommodated; a gear case which is fixed to a front face of the motor case; and a control board which controls the motor, wherein the deceleration mechanism is an one-stage deceleration mechanism having: the first gear serving as an input gear; and the second gear serving as an output gear, characterized by: the second gear is a sector gear, the control board is disposed in front of the motor and above the deceleration mechanism, and is covered with a circuit board cover, and the motor case, the gear case, the rotation member and the control board are disposed within a range of an axial dimension of the rotation shaft in the direction along the rotation shaft. the second gear is a sector gear, the control board is disposed in front of the motor and above the deceleration mechanism, and is covered with a circuit board cover, and the motor case, the gear case, the rotation member and the control board are disposed within a range of an axial dimension of the rotation shaft in the direction along the rotation shaft.