Abstract: An object of the present invention is to enable 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 sensing target, to easily and accurately grasp information peculiar to the crystal sensor, for instance, information regarding a quality thereof. As a concrete means for solving the problem, it is designed such that 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.