A control device of a cutting tool is revealed. For performing cutting, opening and closing, the cutting tool includes a pair of handles pivotally connected to each other and each handle having a blade. The control device is set on the handle and involved in opening or closing of the blades of the cutting tool. The control device includes a first component and a second component. The first and the second components are connected to and locked with each other tightly by a fastening structure. The control device is disposed on the handle closely, without loosening from the handle.