To prevent thickening of a segment constituting a primary lining body and to implement a possibility of thinning a secondary lining body.

A drainage canal 2 is formed at a joint 1e between a plurality of segments 1a, 1c so as to be closed between a secondary lining side surface 1f of a primary lining body 1 and a natural ground side surface 1g and so as to be extended along the joint 1e. Therefore, water infiltrated from the natural ground into the joint 1e is introduced via the drainage canal 2 to an invert portion of the primary lining body 1, whereby the water can be prevented from leaking into a joining surface between the primary lining body 1 and a secondary lining body.