PURPOSE: To provide an economical and high performance method for detecting a paint film to defect pinholes in the insulating paint film which can be detected with simple procedures after the execution of a conductive film painting.

CONSTITUTION: In an ocean life deposite preventing device provided with a conductive paint film executed through an insulating paint film on a contact part of the sea water with a metallic outer plate in an ocean structure, when the defective execution part of the insulating paint film 2 is detected after the execution of the conductive paint film 3, voltage 8 is applied between the conductive paint film 3 and the outer plate 1 to detect the flow direction of short current to the defective execution part and generate heat caused by the short current so that an amount of infrared ray generated by the heat generation is measured to detect the defective execution part of the insulating paint film 2.