To securely decide that information on a medium is original by including a write stage wherein an image of the information is generated by encoding the information and written in an accessible memory area of a particle article.

To write the information 'I' in a step (a), it is transferred to the accessible memory area At of the portable article 1. Then the information stored in the accessible area At is encoded in a step (b) by a processing circuit 21 by using a program stored on a terminal 2. In a step (c), its intermediate result R1i is sent to the processing circuit 12 of the portable article 1 and in this processing circuit 12, an encoding function Fc implemented by a program is applied thereto. An image 'I'' is transferred in a step (d) and written in the accessible memory area Ac of the portable article l, and this area includes the information 'I' and its image 'I''.