A throttle device comprising: a plurality of throttle units (11, 12) providable in an engine for each of cylinders or for each of cylinder groups, each of the throttle units (11, 12) including a throttle body having intake air passages (13a, 13b, 13c, 13d) corresponding to the plurality of cylinders (2a, 2b, 2c, 2d) of the engine, a throttle shaft rotatably supported by the throttle body, throttle valves (16a, 16b, 16c, 16d) secured to the throttle shaft to open and close the intake air passages (13a, 13b, 13c, 13d) for the cylinders (2a, 2b, 2c, 2d), a motor, a decelerator (20, 45) decelerating rotation of a drive shaft of the motor and transmitting the decelerated rotation to the throttle shaft, wherein a deceleration ratio of the decelerator provided in a first throttle unit and a deceleration ratio of the decelerator provided in a second throttle unit out of the plurality of throttle units (11, 12) are different from each other, and a cylinder deactivation control unit stopping operations of the motor of the second throttle unit out of the first throttle unit and the second throttle unit to cause the throttle valves (16c,16d) of the second throttle unit to have a predetermined degree of opening in a predetermined operation region of the engine and deactivating combustion of the cylinders or the cylinder groups (2c,2d) corresponding to the second throttle unit, and wherein the deceleration ratio of the decelerator in the second throttle unit is lower than the deceleration ratio of the decelerator in the first throttle unit, wherein in the deactivated state, the throttle valves of the deactivated cylinder are fully opened. a plurality of throttle units (11, 12) providable in an engine for each of cylinders or for each of cylinder groups, each of the throttle units (11, 12) including a throttle body having intake air passages (13a, 13b, 13c, 13d) corresponding to the plurality of cylinders (2a, 2b, 2c, 2d) of the engine, a throttle shaft rotatably supported by the throttle body, throttle valves (16a, 16b, 16c, 16d) secured to the throttle shaft to open and close the intake air passages (13a, 13b, 13c, 13d) for the cylinders (2a, 2b, 2c, 2d), a motor, a decelerator (20, 45) decelerating rotation of a drive shaft of the motor and transmitting the decelerated rotation to the throttle shaft, wherein a deceleration ratio of the decelerator provided in a first throttle unit and a deceleration ratio of the decelerator provided in a second throttle unit out of the plurality of throttle units (11, 12) are different from each other, and a cylinder deactivation control unit stopping operations of the motor of the second throttle unit out of the first throttle unit and the second throttle unit to cause the throttle valves (16c,16d) of the second throttle unit to have a predetermined degree of opening in a predetermined operation region of the engine and deactivating combustion of the cylinders or the cylinder groups (2c,2d) corresponding to the second throttle unit, and wherein the deceleration ratio of the decelerator in the second throttle unit is lower than the deceleration ratio of the decelerator in the first throttle unit, wherein in the deactivated state, the throttle valves of the deactivated cylinder are fully opened.