To prevent contamination of a work environment due to leak and to allow leak detection regardless of material or shape of a pipe when the leak of the pipe is detected by a chemical method.

In this leak detecting tube 1, a detecting layer 3 changing in color due to gas, liquid, or chemical reaction is disposed inside transparent or translucent heat shrinkable tube layer 2 of which tube diameter is decreased by heating, the pipe is inserted into the tube and adhered to it by heating, and a leaking part of gas or liquid leaking from the pipe is detected based on the change in color of the detecting layer 3.