A fastening device includes a head member and a body member. The head member has a stem portion provided with a fastening section; and the body member is movably assembled to the head member and includes an elastic fastening section for engaging with a first workpiece. To connect the first workpiece to a second workpiece, simply fasten the fastening section of the stem portion to the second workpiece. To disconnect the first workpiece from the second workpiece, simply release the fastening section from the second workpiece. With these arrangements, it is able to quickly connect and easily disconnect two workpieces to and from one another.