A loading mechanism includes a fastening board, a cam, a rotary pivot, and a load module. The fastening board defines a pivot hole at the center portion of the fastening board and a sliding guide adjacent to the pivot hole. The cam defines a locating hole and an annular guide. The load module includes two guiding poles, a follower fastened to one end of the two guiding poles, and a clamping member fastened to the other end of the two guiding poles. The distance between a part of the annular guide and the locating hole is gradually decreased, and the cam can be driven to rotate. The cam drives the follower to slide along the annular guide to drive the load module to slide along the sliding guide.