Membrane defect inspection method and membrane defect inspection device

A membrane defect inspection method for a membrane module set comprising a plurality of membrane modules connected in parallel under a straight pipe portion of gas detection piping extending in a first direction, all of the membrane modules being continuously arranged under the straight pipe portion at intervals along the first direction, and the straight pipe portion communicating with primary spaces in each of the plurality of membrane modules to which raw water is supplied or secondary spaces in each of the plurality of membrane modules from which treated water is extracted after the raw water is filtrated by membranes, the method comprising:

• a gas injection process where gas is injected into spaces opposite to the primary spaces or the secondary spaces communicating with the gas detection piping in the plurality of membrane modules while the gas detection piping is filled with water;
• and
• an echo detection process where an ultrasonic sensor comprising an ultrasonic transmitting section and an ultrasonic receiving section is brought into contact with an end portion of the straight pipe portion of the gas detection piping extending in the first direction, and a reflected wave of an ultrasonic wave transmitted from the ultrasonic transmitting section along a longitudinal axis of the straight pipe portion parallel to the first direction, is detected by the ultrasonic receiving section.