Method of testing for a leak with the inner vessel of a double blow molded bottle

Double blow molded bottles of synthetic resins are given consistent quality by making it possible to detect the existence of a leak in the inner vessel in which to store the liquid contents. The bottles of consistent quality can be provided by a method of leak test, which includes forming an air channel between an outer vessel and an inner vessel by deflating and peeling the inner vessel from the outer vessel and by securing air flow through an opening of an air channel and judging the existence or non-existence of a leak through the wall of the inner vessel by supplying air to the inner vessel at a given micropressure and by observing, after a certain period of elapsed time, whether or not the pressure inside the inner vessel reaches the predetermined level which has been set from a test conducted under the same conditions using the bottles with no leak through the wall of the inner vessel.