PURPOSE: To provide a seam ironing device for automatically performing the manual work of opening the seam allowance of trousers and stretching the wrinkles, which was possible only on a horizontal ironing board and required a relatively wide work place before.

CONSTITUTION: This seam ironing device is the one for stretching the wrinkles of the seam allowance inside clothes and is provided with a tension device provided with a pair of tractors 2 for pulling the clothes and a pair of iron rollers 3 facing each other. The iron rollers 3 add a pressure to each other under an initial load, and moved along a seam 7 to be ironed, are rotated on the seam 7 and thus open and iron the seam allowance so as to be flat. The seam ironing device is appropriate for the production of read-to-wear clothes especially since it excellently finishes the seam allowance.