A sprayer can convert the entire manual effort used to operate a manual pump into energy for spraying liquid. The sprayer has a liquid tank filled with a liquid, and an air tank having a pressurized air supply valve through which pressurized air can be introduced into the air tank. The air tank communicates with a float valve having a valve hole communicating with a spray nozzle and a hollow rod as the outlet of a manual pump. Pressurized air is introduced into the air tank through the pressurized air supply valve to increase the air pressure in the tank to a predetermined bias pressure. Then, the manual pump is operated to suck liquid in the liquid tank and supply the thus sucked liquid through the float valve into the air tank.