To produce a flanged pipe unit, a separate flange (1) is put on a pipe (5) and then the pipe is subjected to a punching to achieve an interlocked connection between the flange and the pipe. The flanged pipe unit produced by the method of the invention comprises a metal pipe including a larger expanded portion (5a), a smaller expanded portion(5b) and a raised portion (5b') which are axially aligned so that the smaller expanded portion is placed between the larger expanded portion and the raised portion (3); and a metal flange having a through bore (2) through which the pipe passes, the through bore including a larger diameter portion (3), a smaller diameter portion (4) and a tapered end portion (4a) which are axially aligned so that the smaller diameter portion is placed between the larger diameter portion and the tapered end portion. The larger expanded portion, the smaller expanded portion and the raised portion of the pipe are intimately engaged with the larger diameter portion, the smaller diameter portion and the tapered end portion of the through bore respectively thereby to establish a dove-tail coupling between the pipe and the flange.