The present invention is a modular stock system for rifles. Each of the contacts includes a main part, two bowed wing parts located at both sides of the main part, two elastic arms extended upward from one end of each wing part, two clamp parts at the upper edge of the elastic arms and a bearing part for adhering a tin ball. A discharge circuit discharges the global read line if any one of a plurality of the sense amplifiers is enabled and is outputting a signal having a first digital logic value onto an input lead of the discharge circuit. The insertion key can be inserted into the insertion hole. In the case of separating the movable electrode plate 12 from the stationary electrode 84a, a voltage is applied between them.