Abstract: An acoustic pipe length measuring apparatus for measuring the length of a pipe-like member in accordance with the time between the emission of a pulse-like sound wave from a speaker at one end thereof and the collection of sound waves reflected at the other end thereof, by a microphone, and a sonic velocity, in which data of a sonic velocity at a reference temperature of a gas present in the pipe-like member is stored in memory, and a sonic velocity value at a temperature of gas detected in the pipe-like member is computed with the use of the data of a sonic velocity value which is read from the memory in accordance with a kind of gas in the pipe-like member, thereby it is possible to calculate the length of the pipe-like member from the sonic velocity value obtained through the computation and the above-mentioned time.