To provide a back pack type power sprayer whose back contact pad is formed to be curved in the back side direction from an approximately lateral center to an end portion.

This back pack type power sprayer is characterized by adhering a back contact pad 33 to the back pack portion 2b of the back pack type power sprayer 1, disposing portions 34 for attaching back pack belts in the upper portion of the back contact pad 33, and smoothly forming the back pack portion 2b in an approximately S-shape on the side view, wherein the upper portion 33a of the back contact pad 33 is curved on the side of an engine 5 in the front direction from the upper portion to the lower portion, and projected in the back direction with the shift to the lower portion 33b, so that the lower portion where a pump device 4 and the like are disposed is more projected in the backside direction than the upper portion where a chemical liquid tank 3 and the like are formed.