Provided is an ultrasonic flow sensor with improved practicality. An ultrasonic wave is transmitted and received by an ultrasonic element. A first flow rate value of a fluid in a pipe is calculated based on a propagation time difference of an ultrasonic signal, a measurement value corresponding to an ultrasonic velocity, and a parameter for identifying an inner diameter of the pipe. A second flow rate value of the fluid in the pipe is calculated based on a frequency shift of the ultrasonic signal and the parameter. The first flow rate value is calculated using a propagation time of the ultrasonic signal as the measurement value in accordance with a correspondence relationship among a distance of a path through which the ultrasonic wave propagates through the fluid in the pipe, a time for which the ultrasonic signal propagates in the path, and the ultrasonic velocity.