An ion concentration measuring device that measures the concentration of ions contained in a solution, comprising: an ion detection element for generating a first potential based on the concentration; a first electrode for outputting the first potential; a memory for storing data; a reader-writer for writing data to the memory or reading data from the memory; and a controller adapted to use the first potential to calculate the concentration, wherein the ion detection element and the memory are installed in a first cartridge, the memory has a normal mode in which normal power is supplied and a standby mode in which the supply of power is suppressed, the controller is adapted to set the memory to the normal mode in a memory access period which excludes a potential measurement period for which the controller acquires a potential value corresponding to the first potential output by the first electrode, and the controller is adapted to set the memory to the standby mode when the memory access period is complete, characterised in that the ion concentration measuring device further comprises: a temperature sensor for measuring a peripheral temperature around the ion detection element; and a temperature control device adapted to adjust the peripheral temperature around the ion detection element in accordance with the result of the detection by the temperature sensor, wherein the controller is adapted to reduce the rate of the writing to the memory as the peripheral temperature around the ion detection element detected by the temperature sensor exceeds a temperature suitable for measurement by the ion detection element, to suppress the amount of heat generated from the memory in the writing of the data to the memory. an ion detection element for generating a first potential based on the concentration; a first electrode for outputting the first potential; a memory for storing data; a reader-writer for writing data to the memory or reading data from the memory; and a controller adapted to use the first potential to calculate the concentration, wherein the ion detection element and the memory are installed in a first cartridge, the memory has a normal mode in which normal power is supplied and a standby mode in which the supply of power is suppressed, the controller is adapted to set the memory to the normal mode in a memory access period which excludes a potential measurement period for which the controller acquires a potential value corresponding to the first potential output by the first electrode, and the controller is adapted to set the memory to the standby mode when the memory access period is complete, characterised in that the ion concentration measuring device further comprises: a temperature sensor for measuring a peripheral temperature around the ion detection element; and a temperature control device adapted to adjust the peripheral temperature around the ion detection element in accordance with the result of the detection by the temperature sensor, wherein the controller is adapted to reduce the rate of the writing to the memory as the peripheral temperature around the ion detection element detected by the temperature sensor exceeds a temperature suitable for measurement by the ion detection element, to suppress the amount of heat generated from the memory in the writing of the data to the memory. a temperature sensor for measuring a peripheral temperature around the ion detection element; and a temperature control device adapted to adjust the peripheral temperature around the ion detection element in accordance with the result of the detection by the temperature sensor, wherein the controller is adapted to reduce the rate of the writing to the memory as the peripheral temperature around the ion detection element detected by the temperature sensor exceeds a temperature suitable for measurement by the ion detection element, to suppress the amount of heat generated from the memory in the writing of the data to the memory.