Operation assistance system and control device

The invention provides an operation assistance system and a control device, which can restrain false detection of manual operation and false operation of auxiliary action. An operation assistance system according to an embodiment is provided with: a sensor that detects acceleration applied to an opening/closing unit; a drive unit for generating a driving force for moving the opening/closing portion; a manual operation detection unit that detects, on the basis of the acceleration detected by the sensor, a manual operation for opening or closing the opening/closing unit by applying a force to the opening/closing unit by a user; and a drive control unit that, when a manual operation is detected, controls the drive unit so as to reduce the user operation force required for the manual operation, and when the difference between the acceleration applied to the opening/closing unit and the average acceleration is equal to or greater than a first threshold value, determines that the manual operation has been performed