PURPOSE: To turn an arm at constant and high speeds shocklessly by providing a load uniformalizing mechanism to deny automatically and continuously the rotation moment based on the arm gravity/the weight of a functional tool.

CONSTITUTION: At the time when an arm 72 is turned by a certain angle, a 1st link bar 101 in a load uniformalizing mechanism 100 is also turned concentrically just as its phase shifting by the same angle in the same direction. On the other hand, a 2nd link bar 103 is telescopicalbe, the tip part is supported with its rotation on the tip part of the 1st link bar 103 and the base end part is rotatably supported on the axial line which passes through the rotation center of the arm 72. Also, an energizing means 106 energizes the 1st link bar so as to apply an external force on the tip of the 1st link bar 101. Consequently, the rotation moment based on the arm gravity, etc., is denied while the arm is turned from the horizontal state to the vertical state and the load moment of a driving source becomes minimum and uniform. The arm is therefore reciprocated with its turning without shock at constant speed and high speed.