A lamp includes a lamp head, a lamp rod and a fastening device fixing the lamp head onto the lamp rod. The fastening device includes a tube-shaped lamp seat extending from the lamp head, a tightening device disposed in the lamp seat, a connecting device connecting the tightening device to the lamp seat, and a locking device mounted to the lamp seat. The tightening device includes an inner face and an outer face opposite to the inner face. The inner face of the tightening device and an inner face of the lamp seat sandwiching an end of the lamp rod therebetween. The tightening device can move along a radial direction of the lamp seat. The locking device presses the tightening device toward the end of the lamp post to urge the tightening device to tightly press the lamp rod.