A distance measuring system comprising: a transmitter that simultaneously emits an infrared radiation and an ultrasonic wave; and a receiver that include a table showing a relationship between an arrival time, indicative of a period from detection of the received infrared radiation to detection of the received ultrasonic wave, and a required received signal strength of the ultrasonic wave corresponding to the arrival time when the ultrasonic wave is directly received, that compares the received signal strength of the ultrasonic wave with a required received signal strength corresponding to the arrival time retrieved from the table, and that calculates the distance to the transmitter based on the arrival time when the received signal strength of the ultrasonic wave is higher than the required received signal strength corresponding to the arrival time retrieved from the table.