To feed lubricating oil to whole part of the cylinder in a power sprayer having such a structure that a fixed amount of lubricating oil is collected in a driving case housing a pump driving part, the cylinder facing substantially horizontal direction is provided in the case, and a piston is substantially horizontally reciprocated in the cylinder by the pump driving part.

A lubricating oil suction port 2c located below lubricating oil level L and a lubricating oil discharge port 2d located above the lubricating oil level L are formed at a lower end of the cylinder 2b. The suction port 2c is formed in, for example, a bottom part or a side face part of the cylinder 2b to communicate the cylinder 2b with a crank chamber 2a when the piston 6 reaches a bottom center and its vicinity. The discharge port 2d communicates the cylinder 2b with the crank chamber 2a in the whole reciprocating stroke of the piston 6 and is formed, for example, at an upper end of the cylinder 2b.