The present invention provides a pipe body of which the edge sections contact with each other stably and which can be formed only by means of only a press processing without performing a welding in mass-producing, wherein separation-prevented engagement due to deformation of at least one of the engagement sections absorbs the spring back in the press processing. Also, the present invention provides a pipe body, a metal plate for the pipe body and a forming method of the pipe body using the sheet metal for the pipe body. The pipe body includes a pair of edge sections 1e, 1f forming closed end surface by means of contact with each other, wherein surroundings of each edge sections 1e, 1f form a plane 1a jointly when each edge sections 1e, 1f are in contact with each other, and at the same time, engagement sections consisting of female engagement section 1g and male engagement section 1h engaged with each other are formed in the edge sections 1e, 1f, and the edge sections 1e, 1f get in contact with each other closely by means of separation-prevented engagement due to deformation of at least one of the female and male engagement sections 1g, 1h.