A water gun discharges water continuously by pushing in and pulling out an operating portion and has a casing imitating a barrel, a rear grip portion and a front grip portion. The casing incorporates a pump mechanism and includes pumping tubing forming a pumping path through which water is pumped up from a water storage tank by the pumping mechanism and a muzzle portion disposed at a front end of the casing. The pump mechanism includes a first cylinder and a second cylinder which are oriented in opposite directions, a first piston slidable forwards and backwards within the first cylinder and a second piston slidable forwards and backwards within the second cylinder, an interlocking member coupled to the first piston and the second piston and brought into engagement with a rear half portion of the casing, pumping check valves, a jet water flowing chamber and a water supply path.