A balancer mechanism for a rotating shaft is configured to prevent deviation of the axis of the rotating shaft. The balancer mechanism (20) has an assistance torque generation device (21) for generating an assistance torque. The assistance torque generation device (21) includes a cam member (24) fixed to the rotating shaft (4), a cam follower member (25) and a gas spring (27). The balancer mechanism has a reaction force generation device (22) provided for generating, a balancing moment on the rotating shaft that cancels out a tilting moment that tilts the rotating shaft (4) around a bearing member (9) in a direction to separate it from the assistance torque generation device (21) and which is caused by the biasing force of the gas spring (27).

A balancer mechanism for a rotating shaft is capable of preventing deviation of the axis of the rotating shaft. The balancer mechanism (20) has an assistance torque generation means (21) for generating an assistance torque; the assistance torque generation means (21) includes a cam member (24) fixed to the rotating shaft (4), a cam follower member (25) and a gas spring (27); and a reaction force generation means (22) is provided for generating, by the biasing force of the gas spring (27), a balancing moment that cancels out a tilting moment that tilts the rotating shaft (4) around a bearing member (9) in a direction to separate it from the assistance torque generation means (21).

A counterweight mechanism for a swivel arrangement includes first and second counterweights each including a seat, an axle, and two cylinders. The swivel arrangement has one end adjacent to the axle. The axle is rotatably, partially disposed in the seat. Each cylinder has a first end pivotably secured to a position proximate to the axle and a second end pivotably secured to the seat.

The present invention includes a table (2) for placing a workpiece (Wa) thereon, a supporting mechanism (10) including a rotary shaft (15, 16) and supporting the table (2) so as to be able to rock the table (2) about an axial center of the rotary shaft (15, 16), a first drive motor (20) rotating the rotary shaft (15) of the supporting mechanism (10) to rock the table (2), a balance imparting mechanism (30) imparting a balance load to the rotary shaft (15) in accordance with a position of rocking of the table (2), and a controller (50) controlling the first drive motor (20). The balance imparting mechanism (30) includes an eccentric disc (31) having a circular plate shape and connected at a position eccentric from a center thereof to the rotary shaft (15), a housing (32) holding an outer periphery of the eccentric disc (31) via a bearing (33), and a load imparting unit (35) imparting the balance load to the housing (32) in a direction intersecting an axis of the rotary shaft (15).