A clamping device includes a first clamping arm and a second clamping arm, an arm driving portion for displacing the first clamping arm to a clamping position and a non-clamping position, and a clamping force applying portion for applying a required clamping force to the clamping arm. The arm driving portion has a first driving source for displacing the first clamping arm and a power transmission mechanism. The clamping force applying portion has a pressing member for applying the clamping force to the first clamping arm by applying a rotating force in a clamping direction to the rotary shaft and a second driving source for displacing the pressing member from a non-operating position to an operating position for applying the clamping force.