An injection unit in which an offset load is not applied to a ball screw for moving an injection screw. A pusher plate is provided that is moved while being guided by guide rods extending between front and rear plates, and is mounted with the injection screw and the ball screw so as to be rotatable but axially immovable. The ball screw is threadedly engaged with a nut mounted to the rear plate so as to be unrotatable and axially immovable. A support plate is coupled through coupling rods to the pusher plate. The ball screw has another end supported on the support plate in a rotatable but axially immovable manner. The pusher and support plates are supported on a base by linear motion guides. The ball screw is supported at its both ends by the pusher and support plates so as not to be tilted, whereby no offset load is produced and the service life is prolonged.
