A lamp includes a shell with an assembling portion, a main body disposed in the shell, and a torsion spring. The torsion spring includes a spring body, a first supporting part, and a second supporting part. The spring body is assembled to the assembling portion. The first supporting part includes a first arm connected to an end of the spring body, a second arm near another end of the spring body and a first bending part connected between the first supporting part and the second supporting part. A structure of the second supporting part is similar to that the first supporting part and is connected to the spring body. The first supporting part and the second supporting part are suitable for tightly clamping the assembling portion and a fixing end respectively by the force of the spring body.