To make it possible to inspect a desired range of a container to be inspected in a narrow place, reduce the influence of the size of the narrow place and improve the freedom in inspection operation.

A structure Z surrounding a container X is equipped with a travel guide groove (a) directing inward along a peripheral direction, while an inlet path (b) connected from above is placed on the travel guide groove (a). An inspection instrument A is guided by the travel guide groove (a) and the inlet path (b), wherein the inspection instrument A has a carrier 1 traveling in an axial direction, a carrier 2 traveling in a peripheral direction which is separably connected to the carrier 1 and travels in the peripheral direction and a flaw detection mechanism 3 mounted on the carrier 2.