A tool attachment unit includes a power feeding electrode and a plurality of detection electrodes. When a tool including a power receiving electrode and a displacement electrode is attached onto the tool attachment unit, the power feeding electrode and the power receiving electrode are opposed to each other, and the detection electrode and the displacement electrode are opposed to each other. A pair of the power feeding electrode and the power receiving electrode and a pair of the detection electrode and the displacement electrode form a capacitor circuit. A capacity of the capacitor circuit is changed in response to a position of the tool. A tool position detection unit supplies a power feeding signal to the power feeding electrode. A voltage information extractor extracts voltage information from the detection electrode. Based on the extracted voltage information, a position detection/arithmetic operation unit detects to which position the tool is attached.