A wireless tag adjusting method comprising measuring a communication characteristic by performing wireless communication with a wireless tag having an antenna and an integrated circuit connected to the antenna, calculating an antenna adjustment pattern on the basis of the measured communication characteristic, and forming an adjustment pattern by one of or a combination of ejecting of a dielectric material, ejecting of a magnetic material, and ejecting of a conductive material by using an ink jet printer on and/or around the antenna in the wireless tag in accordance with the calculated antenna adjustment pattern, thereby adjusting the antenna in the wireless tag.