To sense (monitor) a state of tension of a patient by measuring a physiological state such as a blood pressure, a pulse rate or the like during the treatment as well as before the treatment of the dental treatment to apply a kind of stimulus on the patient to relax the patient when the state of tension is judged to be abnormal.

A dental treatment chair includes a monitoring means (a finger cuff 17) to measure the physiological state of the patient such as the blood pressure, the pulse rate or the like and a stimulus applying means such as an airbag to apply the stimulus on the patient. When the physiological state (the state of tension) of the patient reaches a prescribed value or higher, the above stimulus applying means is driven to apply the stimulus on the patient to relax the patient.