To provide a method and a system for judging genuineness when an imitation coloring material cartridge of printer, other than a specified product, having a resembling appearance but using an easy-to-judge amorphous alloy material is set.

Genuine coloring material cartridges 2 and 3 are fixed with an amorphous magnetic body 9. The printer body is provided with a coil 10 for exciting the amorphous magnetic body of a coloring material cartridge fixed to the printer body with an AC magnetic field, and a coil 19 for detecting the AC magnetic field passed through the amorphous magnetic body 9. A decision is made wether the coloring material cartridges 2 and 3 are imitation or not based on the fact wether a magnetic pulse superposing a detection signal of the detection coil 19 generated at a specified level of the AC magnetic field is generated at a specified phase position in the period of the AC magnetic field.