1. A selector pen for touch screen, comprising a barrel, a transparent head connected to a front end of said barrel, a light-emitting means mounted in said barrel behind said transparent head, a switch rotatably connected to a rear end of said barrel for turning said light-emitting means on and off; said switch including a base defining a hollow insertion hole therein, a movable rod received in said insertion hole of said base, and a cap rotatably covered onto said base; said movable rod including a head portion having an inclined top, and a long body portion below said head portion; one half of said inclined top being cut to form from top to bottom into a spiral guide surface, and the other half of said inclined top being formed into a raised side stop; an upper and a lower recess being provided at upper and lower ends, respectively, of an intersection line between said spiral guide surface and said raised side stop; and said long body portion having a configuration corresponding to said insertion hole defined in said base for inserting into said insertion hole to only move upward and downward relative to said base but not rotate in said base; and said cap being configured for rotatably covering onto said base and defining an inner space, said inner space being provided in an upper half with a radial projection that is adapted to slide along said spiral guide surface on said inclined top of said movable rod to finally engage with said upper or said lower recess at two ends of said spiral guide surface when said cap is rotated relative to said base.
2. The selector pen for touch screen as claimed in claim 1, wherein said base of said switch is provided at predetermined positions with a plurality of radially protruded rings, and said cap of said switch is provided around said inner space at predetermined positions with a plurality of annular grooves corresponding to and adapted to engage with said radially protruded rings on said base.
3. The selector pen for touch screen as claimed in claim 1, wherein said hollow insertion hole defined in said base has a non-circular cross section.