An object of the present invention is to provide a number-of-step detection system, a number-of-step detecting method, and a pedometer capable of accurately detecting the number of steps in correspondence with the walking characteristics of an individual.Vibration data acquired with a vibration data acquiring unit of a pedometer is transmitted from the pedometer to a server with a communication unit, and number-of-step decision criterion data suited for measuring the number of steps is calculated with the calculation unit of the server based on the vibration data. The number-of-step decision criterion data calculated in the server is transmitted from the server to the pedometer, and the number-of-step decision criterion data stored in the pedometer is updated to the number-of-step decision criterion data calculated by the server to accurately count the number of steps in correspondence with the walking characteristics of the individual.