Abstract: A system for measuring and controlling the concentration of an emulsion, wherein a measuring pipe included in an emulsion feed line is fitted with an emulsion concentration-detecting device; the ultrasonic wave transmitter of the concentration-detecting device sends forth ultrasonic waves into an emulsion running through a circulation line so as to be caught by an ultrasonic wave receiver; the concentration-detecting device generates an output signal corresponding to the velocity with which ultrasonic waves are propagated from the ultrasonic wave transmitter to the ultrasonic wave receiver, utilizing the fact that the velocity of said propagation is substantially proportional to the concentration of an emulsion flowing through the circulation line, and also delivers an output signal corresponding to temperature variation from a detection terminal through a transducer to a circuit for correcting the measured concentration of the emulsion according to temperature variation in view of the fact that the propagati