PURPOSE: To save labor and the number of persons in leakage detection, by generating pressure waves in a liquid at a position in a liquid transporting pipe, propagating the pressure waves to the leaking position of the pipe, and capturing the reflected waves generated at the leaking position.

CONSTITUTION: Under the state an electromagnetic valve 3 is opened and part of liquid in a pipe 1 flows through a branch pipe 2, the electromagnetic valve 3 is closed. The flow into the branch pipe from the pipe 1 is suddenly stopped. Therefore pressure increase is yielded, and pressure waves are propagated in the pipe 1. The pressure is measured by a pressure detector 4. When the pressure waves reach a leaking position (a), reflected waves are generated. When the reflected waves reach the pressure detector 4, the pressure is measured. Based on the time difference between the passage of the outgoing waves of the pressure waves at the pressure detector and the passage of the reflected waves from the leaking position (a), the distance between the pressure detector 4 and the leaking position (a) can be found. Thus the saving of labor and the number of persons in the leakage detection can be accomplished.