An apparatus for measuring a bending angle between two portions of a workpiece in a bending machine includes at least a motion sensor unit provided with a gyroscope sensor, a processing unit connected with the gyroscope sensor and a coupling device for connecting the motion sensor unit with a portion of the workpiece to be bent. During a bending operation of the workpiece the gyroscope sensor measures at least one angular velocity and a related rotation angle of the portion according to an axis and the processing unit receives data from the gyroscope sensor regarding the rotation angle in order to calculate the bending angle as a function of the rotation angle.