To make it difficult for a third party to analyze and acquire an operational expression required to determine whether or not a consumable supply is a genuine product, and to produce a non-genuine product completely replacing the genuine product even if the operational expression is analyzed by the third party.
A determination method comprises: a step (S2) that a reader-writer reads solid identification information and additional information from a storage medium, at the time of attaching a consumable supply (S1); and steps (S6, S7 and S10) that a control part determines whether the attached consumable supply is a genuine product or not by selecting an operational expression in accordance with a result obtained by masking the solid identification information read by the reader-writer, by conducting operation with the solid identification information in accordance with the selected operational expression, and determining whether or not the operation result is consistent with determination information included in the additional information read by the reader-writer.
Inoue On
Nishimori Norio