A child unit (30) is configured to freely pivot about a first axial center (AX1) relative to a parent unit (10), and a grandchild unit (50) including a manipulator (56) is configured to freely pivot about a second axial center (AX2), which is orthogonal to the first axial center (AX1), relative to the child unit (30). A first rotary volume (32) is configured to detect a relative pivot amount of the parent unit (10) and the child unit (30) about the first axial center (AX1), and a second rotary volume (39) is configured to detect a relative pivot amount of the child unit (30) and the grandchild unit (50) about the second axial center (AX2). Both the first rotary volume (32) and the second rotary volume (39) are mounted to an electrical circuit board (43) of the child unit (30).