Disclosed are a pH or concentration measuring device and a pH or concentration measuring method which enable measurement in the shortest possible time even in an object to be measured having low buffer capacity. Specifically disclosed are a pH or concentration measuring device and measuring method for measuring the pH or concentration of a sample solution that is an object to be measured, the device being provided with first and second sensors that each output a signal corresponding to the pH or concentration of a solution, an inspection tube that is provided with a first room in which the first sensor is disposed and a second room in which the second sensor is disposed, a feeding means that feeds a baseline solution into the inspection tube, and an injecting means which injects the sample solution into the first room of the inspection tube and brings the sample solution into contact with the first sensor, wherein a vibration means which vibrates the interface between the sample solution stored in the first room and the baseline solution is provided.