PURPOSE: To detect easily an outbreak place of a leakage, by applying pulse voltage to the one end of an embedded conductive body and measuring the time required for returning the pulse voltage to the other end.

CONSTITUTION: At first, a detection apparatus 9 is made ot operate and pulse voltage is outputted from a pulse transmission part 10 at a prescribed time interval. On occasion of not taking place a leakage, the pulse voltage is not received by a pulse reception part 11 because heat insulating materials 4, 6 are electrically nonconductive bodies. On occasion of the leakage taking place, the first and second conductive bodies 7, 8 are short-circuited by a leaking liquid at an outbreak place of the leakage. Accordingly, the part 11 receives the pulse voltage. The value divided the product of propagating velocity of the bodies 7, 8 and time from the transmission to the reception of the pulse voltage into two, is nearly equal to the distance between the leaking place and one end of the bodies 7, 8 because the pulse voltage outputted from the part 10 is transmitted to the part 11 propagating the second conductive body 8, a short-circuit place by the leakage and the first conductive body 7.