A supporting mechanism of an observation system for dental and medical treatment three-dimensionally movable supports a display unit for stereoscopically displaying an observation image of a surgical microscope regarding treatment of a patient on a dental chair and holds the display unit in an observation position of a dental surgeon keeping a constant posture. In a state where a vertically holding arm has been moved to a position where a vertical axial line thereof passes through an oral cavity of the patient, the supporting mechanism supports the display unit so as to be movable for positioning via a vertically fixed arm and a horizontally pivoting arm, in a position around the dental chair corresponding to a predetermined pivoting radius defined by a horizontal distance up to a finder of the display unit around the vertical axial line.
