PURPOSE: To prevent the generation of an inferior can, by integrating the increment of a paint flow amount due to spray at every spray while comparing the integrated value with a set volue.

CONSTITUTION: Flow meters 3 are respectively connected to spray guns and amplifiers 5 for amplifying the outputs of the flow meters 3 are connected to said flow meters 3 and connected to a microprocessor 7 through an A/D converter 6. The microprocessor 7 subtracts a flow amount in a no-spray state and compares the value obtained by integrating the subtracted value with a reject set value to discharge a spray inferior can to a reject circuit when the integrated value is lower than the set value.