A user, when measuring a sensing target substance in fluid using a crystal sensor (sensing sensor) using a crystal vibrator whose natural frequency is varied by an absorption of the sending target, is able to easily and accurately grasp information peculiar to the crystal sensor, for instance, information regarding a quality thereof. An IC chip in which the information peculiar to the crystal sensor is stored is provided to the crystal sensor, and the peculiar information is read out at a side of a concentration measuring device when the crystal sensor is inserted into the concentration measuring device, and then displayed.