To simplify the interruption and the restart work of spraying by a power sprayer.

In this sprayer, a cylindrical spool body 53, which has the inside diameter composed of a small diameter part 53a at the tip and a large diameter part 53b adjacent thereto and is provided with a relief hole 54 drilled on the large diameter part 53b, is inserted freely movably back and forth into a cylinder chamber 55 provided in one of branched pipes of a downstream side passage of a high pressure chamber 26 for generating a high pressure liquid by the left and right movement of a reciprocally moving plunger 7 and the spoolbody 53 is pressed in the large diameter 53b direction by a pressing spring 56 arranged in the cylinder chamber 55. A high pressure liquid is supplied to a spray hose 35 with a spray nozzle 36 through the inside diameter part of the spool body 53 from the cylinder chamber 55. A by-pass passage 38 opened to the cylinder chamber 55 is connected to the downstream side of a discharge pressure control valve so as to be communicated with a circulating hose 40. When the spray nozzle 36 is closed, the spool body 53 is moved back against the force of the pressing spring 56, and the relief valve 54 and the by-pass passage 38 are communicated with each other.