An apparatus (10) for supporting a medical instrument includes an arm (14), which has a support portion (16) to support a medical instrument (8) at one end, and an intermediate portion of which is supported by a base portion (12) via a support column (20). The arm (14) moves the support portion (16) horizontally and vertically. The apparatus also includes a rotary connecting member (46), which is provided at a second end of the arm (14) and moves to a position corresponding to a position to which the support portion has been moved. The apparatus further includes a counterweight (58), which is connected to the support column (20) to be immovable in the horizontal directions and movable in the vertical directions, and generates vertically downward force. The rotary connecting member (46) is connected to the counterweight (58) so as to be movable in the horizontal directions relative to the counterweight (58) and movable in the vertical directions together with the counterweight (58). When the support portion (16) moves, the rotary connecting member (46) keeps the medical instrument (8) supported by the support portion (16) balanced with the counterweight (58).
