PURPOSE: To give a design having various contents on the surface of a body to be decorated, by a method wherein a thermal head provided with a heating element, which is controlled by a computer control device, abuts against or comes close to the surface of the body to be decorated and a predetermined surface layer part is reacted and changed by heat of the heating element.

CONSTITUTION: A treatment signal such as a picture or a letter corresponding to design contents which are to be given through a computer control device 5 connected with a thermal head 4 is sent to the thermal head 4 by becoming an electric signal and heating of each heating element 3 is controlled corresponding to the electric signal. Then a predetermined treatment signal is sent to the thermal head 4, a predetermined heating element 3 is heated and only a surface layer part 1p of the body 2 to be decorated abutting against a heated heating element 3p is heated and reacted. Since a predetermined part of the surface of the body 2 to be decorated is heated and reacted like this, a surface layer part which is reacted and changed and a surface layer part where neither reaction nor change is performed are formed on the surface layer 1, a reactive part 6 of a heated and changed surface layer is caused to appear as a design, through which surface decoration can be performed.