Abstract: An air motor and an electric painting device improves driving efficiency, and includes a housing, a main shaft inserted inside of the housing, an impeller fixed concentrically with the main shaft to an inserted portion of the main shaft and having a plurality of turbine blades formed on the outer periphery, bearings for rotatably supporting the main shaft and the impeller, and a nozzle having a tubular or hole-shaped channel for ejecting compressed air to the respective turbine blades for rotating the impeller along the circumference. When M1=ve/a0 where ve denotes flow velocity of the compressed air in an entrance of the channel of the nozzle, and a0 denotes acoustic velocity, the length of the channel of the nozzle is set to a dimension of a calculated value or greater using a predetermined expression.