actuator 28 the arm 61 comes into a trajectory 90 along which the horn portion 26 b moves when the carriage arm 26 swings counterclockwise as shown in fig3 the inertia balancing arm 50 includes an elongated arm body 70 a bearing 71 made of synthetic resin and forming an integral part of the arm body 70 near the end thereof facing the y 2 direction a weight 72 fixed to the bottom surface of the arm body 70 at the end thereof facing the y 2 direction and pins 73 and 74 fixedly attached to the y 1 end of the arm body 70 and at some distance from the y 1 end respectively the inertia balancing arm 50 has a size and shape that are balanced around the bearing 71 with respect to swinging movement and has a relatively large inertia moment the z 2 end of the bearing 71 has a protrusion 71 a projecting in the z 2 direction with a cross sectional profile being a semicircle of a radius r 3 and having a ring shape as shown in fig4 the z 1 end of the bearing 71 has a protrusion 71 b projecting in the z 1 direction with a cross sectional profile being a semicircle of a radius r 4 and having a ring shape as shown in fig4 as shown in fig2 a and fig4 the inertia balancing arm 50 is supported to swing around an axis member 81 having a flange portion 81 a that sticks out from the chassis base 21 with a base portion thereof buried therein the inertia balancing arm 50 is positioned close to the actuator 28 the plane in which the inertia balancing arm.