A distance measuring system and a distance measuring method which use a time-of-flight (TOF) method. The distance measuring system obtains a reference light quantity of reflected light which is a cumulative light quantity of the reflected light during a reference period, obtains a measured light quantity of the reflected light which is a cumulative light quantity of the reflected light during a measurement period, and calculates, on the basis of a ratio of the measured light quantity of the reflected light to the reference light quantity of the reflected light and a ratio of the reflected light incident period to the reference period, a reflected light incident period that is a period which is included in the measurement period and during which the reflected light is incident upon photoelectric conversion elements of a light-receiving device. Then, the distance measuring system calculates the distance between the distance measuring system and an object on the basis of the reflected light incident period.