a main scale having a first measuring jaw;

a slider movable relative to the main scale and provided with a second measuring jaw that is abutted to target portions of an object to be measured together with the first measuring jaw;

a display unit that displays a displacement of the slider relative to the main scale;

a feeding mechanism provided on the slider to move the slider along the main scale, the feeding mechanism including:

an outer roller provided on the slider in a manner rotatable around an axis perpendicular to the moving direction of the slider,

an inner roller provided on the slider in a manner rotatable around a rotary axis of the outer roller to be in contact with the main scale, and

a constant-pressure unit that interconnects the outer roller and the inner roller to transmit the rotation of the outer roller to the inner roller and allows free rotation of the outer roller relative to the inner roller when more than a predetermined load is applied on the inner roller, the constant-pressure unit including:

saw-toothed projections provided on an inner circumference of the outer roller, and

a plate spring provided on the outer circumference of the inner roller at a midsection thereof and contacted with the saw-toothed projections of the outer roller on both ends thereof, the both ends extending from a gap between the outer roller and the inner roller in a circumferential direction of the outer roller and the inner roller;

a support unit that interconnects the slider and the feeding mechanism and supports the feeding mechanism in a manner movable toward and away from the main scale; and

a biasing unit that biases the feeding mechanism in a direction away from the main scale.