To prevent double fold lines when applying a fold line to trousers.

A trouser press auxiliary tool 1 is composed of a top layer member 2 a part or all of which is in a transparent sheet or film form, a bottom layer member 4, and a sheet-form middle layer member 3 which is positioned therebetween. The top layer member 2, the bottom layer member 4, and the middle layer member 3 are linearly joined with each other at the end of one side. The top layer member 2, the bottom layer member 4, and the middle layer member 3 tuck the trousers to be pressed, fix the position of the trousers, and prevent double fold lines when pressing the trousers.