And an object thereof is even breakage occurs actuates the dental chair while ensuring proper operation of the safety device therapy provides a dental unit to reduce a situation where break were, of the movable portion detects unintentional contact moving, with a safety device 50 for restricting the rotation, the safety device, the sensor 51, the wiring 52 which is derived from a sensor for detecting an unintended contact, and the wiring is connected, based on the presence or absence of the disconnection of the sensor and wiring a control board 53, which controls the operation of the chair for the patient, the sensor includes a switch 51a which is opened and closed by the presence of unintentional contact, at least two positive electrode side connection portion 51c is disposed on the positive electrode side of the switch, 51d, and at least two negative electrode side connection portion 51e is disposed on the negative electrode side of the switch, it has 51f, resistance to connect one of the one negative electrode side connection portion of the positive electrode side connection portion 51 There is provided in parallel with the switch, wiring is assumed to be a total of at least four derived from each of the two positive electrode side connection portion and the two negative electrode side connection portion of the sensor.断線が生じても安全装置の適切な作動を確保しつつ歯科用椅子を作動させ治療が中断してしまう事態を低減する歯科ユニットを提供することを課題とし、意図しない接触を検知し可動部の移動、回動を規制する安全装置５０を備え、安全装置は、意図しない接触を検知するセンサ５１、センサから導出される配線５２、及び、配線が接続され、センサ及び配線の断線の有無に基づき患者用椅子の動作を制御する制御基板５３、を備え、センサは、意図しない接触の有無により開閉されるスイッチ５１ａと、スイッチの正極側に配置された少なくとも２つの正極側接続部５１ｃ、５１ｄ、及びスイッチの負極側に配置された少なくとも２つの負極側接続部５１ｅ、５１ｆを有し、正極側接続部の１つと負極側接続部の１つとを接続する抵抗５１ｂがスイッチに対して並列に設けられており、配線はセンサの２つの正極側接続部及び２つの負極側接続部のそれぞれから少なくとも合計４本導出されているものとする。
