Camera (1, 41), comprising: a base (3, 43); a cylindrical hollow main body (5, 45) mounted to the base (3, 43); an electric motor (9, 49) supported on a support (7, 47), with an external gear (11, 51) being mounted on an output shaft of the electric motor; a camera head assembly (13, 53), being capable of moving up and down relative to the hollow main body (5, 45) and thus having an extended state and a concealed state, and being capable of rotating horizontally in the extended state, the camera head assembly (13, 53) comprising a cylindrical housing (17, 57), a lens module (19, 59) disposed at least partially in the cylindrical housing (17, 57), and a motherboard (21, 61) for controlling the electric motor (9, 49) and the lens module (19, 59); and an internal gear (15, 55) meshed with the external gear (11, 51); characterized in that one of the support (7, 47) supporting the electric motor (9, 49) and the internal gear (15, 55) is mounted in a fixed manner to the base (3, 43) and located in the hollow main body (5, 45), and the other one of the support (7, 47) supporting the electric motor (9, 49) and the internal gear (15, 55) is mounted in a fixed manner to the camera head assembly (13, 53); and an annular groove (23, 63) and at least one helical groove (25, 65) extending upward from the annular groove (23, 63) are formed on an outer wall of a lower-half part of the cylindrical housing (17, 57) of the camera head assembly (13, 53), a corresponding circular guiding protrusion (29, 69) is disposed on an inner wall of the hollow main body (5, 45), and each said circular guiding protrusion (29, 69) is capable of being received in the annular groove (23, 63) or in the corresponding helical groove (25, 65), a pulling protrusion (31, 71) is formed on the inner wall of the hollow main body (5, 45), a sloping protrusion (33, 73) having an inclined face is formed on the outer wall of the lower-half part of the cylindrical housing (17, 57) of the camera head assembly (13, 53), and when the camera head assembly (13, 53) rotates such that the circular guiding protrusion (29, 69) will enter the helical groove (25, 65) from the annular groove (23, 63), the pulling protrusion (31, 71) applies a downward action force on the inclined face of the sloping protrusion (33, 73), impelling the circular guiding protrusion (29, 69) to enter the helical groove (25, 65) from the annular groove (23, 63), such that up/down movement of the camera head assembly (13, 53) relative to the hollow main body (5, 45) and horizontal rotation of the camera head assembly (13, 53) can be driven by the electric motor (9, 49) alone. a base (3, 43); a cylindrical hollow main body (5, 45) mounted to the base (3, 43); an electric motor (9, 49) supported on a support (7, 47), with an external gear (11, 51) being mounted on an output shaft of the electric motor; a camera head assembly (13, 53), being capable of moving up and down relative to the hollow main body (5, 45) and thus having an extended state and a concealed state, and being capable of rotating horizontally in the extended state, the camera head assembly (13, 53) comprising a cylindrical housing (17, 57), a lens module (19, 59) disposed at least partially in the cylindrical housing (17, 57), and a motherboard (21, 61) for controlling the electric motor (9, 49) and the lens module (19, 59); and an internal gear (15, 55) meshed with the external gear (11, 51); characterized in that one of the support (7, 47) supporting the electric motor (9, 49) and the internal gear (15, 55) is mounted in a fixed manner to the base (3, 43) and located in the hollow main body (5, 45), and the other one of the support (7, 47) supporting the electric motor (9, 49) and the internal gear (15, 55) is mounted in a fixed manner to the camera head assembly (13, 53); and an annular groove (23, 63) and at least one helical groove (25, 65) extending upward from the annular groove (23, 63) are formed on an outer wall of a lower-half part of the cylindrical housing (17, 57) of the camera head assembly (13, 53), a corresponding circular guiding protrusion (29, 69) is disposed on an inner wall of the hollow main body (5, 45), and each said circular guiding protrusion (29, 69) is capable of being received in the annular groove (23, 63) or in the corresponding helical groove (25, 65), a pulling protrusion (31, 71) is formed on the inner wall of the hollow main body (5, 45), a sloping protrusion (33, 73) having an inclined face is formed on the outer wall of the lower-half part of the cylindrical housing (17, 57) of the camera head assembly (13, 53), and when the camera head assembly (13, 53) rotates such that the circular guiding protrusion (29, 69) will enter the helical groove (25, 65) from the annular groove (23, 63), the pulling protrusion (31, 71) applies a downward action force on the inclined face of the sloping protrusion (33, 73), impelling the circular guiding protrusion (29, 69) to enter the helical groove (25, 65) from the annular groove (23, 63), such that up/down movement of the camera head assembly (13, 53) relative to the hollow main body (5, 45) and horizontal rotation of the camera head assembly (13, 53) can be driven by the electric motor (9, 49) alone.