of the variable capacitor varies when pressed by the rear end of the nib 120 a conventionally known pen down switch unit is usable for the pen down switch unit 140 for example either a pen down switch unit capable of detecting variations in a tool force level or an on off type two staged operation pen down switch unit may be used the electronic component unit 150 is made of a plate 151 extending to the rearward of the pen down switch unit 140 on which a printed board 154 is mounted on the printed board 154 are mounted two switching elements 152 and 153 for obtaining switching information and additional electronic components such as coils or capacitors which are connected to or disconnected from the resonance circuit by turning on and off electrical contacts of the respective switching elements 152 and 153 the casing 110 also has a side switch member 160 for turning the switching elements 152 and 153 on and off this side switch member 160 is provided in such a position that a user can easily operate the stylus pen with a forefinger or thumb when holding it like a writing implement normally the side switch member 160 is provided in a position closer to the tip end from the longitudinal center of the stylus pen a pair of knobs 162 and 163 which the user presses to carry out a switching operation are formed on the top surface of the side switch member 160 the knobs 162 and 163 are spaced substantially the same distance apart from the center of the side switch member 160 in this embodiment the knobs are not independent members but portions of the surface of the side switch member.