An air source (11) is connected to an air motor (3) through an electropneumatic converter (12) which is connected to a rotational controller (13). Upon changing settings in a target rotational speed (N0) or paint discharge rate (Q0), in order to supply a necessary air pressure for rotationally driving the air motor (3) in a steady state with new setting conditions, the rotation controller (13) selects a steady value (is) from a rotational data selection processing table, and outputs to the electropneumatic converter (12) the newly selected steady value (is) as an input current value (i). By so doing, the rotational speed of the air motor (3) is quickly controlled toward the changed target rotational speed (N0).