The invention provides an imprinting jig for transferring a pattern onto a thermoplastic sheet. The imprinting jig is provided with: a first die having a surface with a pattern; a die holder for supporting the first die; an elastic member placed between the first die and the die holder; and a second die opposing to the first die. The thermoplastic sheet is placed on the surface with the pattern of the first die. The imprinting jig optionally includes an adhesion reducing means between the elastic member and the first die or between the elastic member and the die holder.