Abstract: An apparatus and method for measuring a specific gravity (concentration) of a medium using an ultrasonic wave, which can measure a propagation velocity of the ultrasonic wave to recognize a change of density and temperature of the medium using the measured propagation velocity of the ultrasonic wave, and for measuring the specific gravity (concentration) of the medium using the recognized change of the density and temperature of the medium. In the apparatus, a controller performs a control operation for displaying at least one medium to be measured on a display unit such that a user can select the medium to be measured, measures a propagation velocity of the ultrasonic wave for the medium selected by the user, reads a conversion equation for a specific gravity (concentration) corresponding to the selected medium, and inputs a value of the measured propagation velocity of the ultrasonic wave into the conversion equation.