PURPOSE: To save water and to speedily conduct a water leak test by forming a water film while sprinkling and circulating a small amount of water, reservoired in a tank body, on the inner peripheral surface, and detecting a water leak place while sending compressed air into the tank body and holding the tank body in the pressure state.

CONSTITUTION: The tank body 12 is formed a completely sealed type which has only one or plural intake outlets 14 formed in the top surface as main openings. Namely, while the intake outlets 14 of the tank body 12 are sealed and the water M reservoired in part of the tank body 12 is sprinkled and circulated on the inner peripheral surface of the tank body 12, the water film W is formed on the inner peripheral surface of the tank body 12 and the compressed air is sent into the tank body 12 to detect the water leak place from the wetting of the water of the water film W to the outer surface of the tank body 12. Consequently, the reservoired water which is required for the water leak test is small in amount and the cost is low; and the need for trouble is eliminated and the water leak test can speedily be conducted.