In the present paper, an equation of the state of compressible hydraulic oils was derived by using the relation between pressure and bulk modulus obtained by Klaus–O’brien. As a result, it was shown that in the case where the bulk modulus was shown by a linear function of pressure, Tait’s equation as an empirical formula was obtained and the constants in the equation were derived theoretically. Further, using the derived equation, the equation of bubble motion was derived by means of an approximate solution using the Poincaré–Lighthill–Kuo coordinate perturbation method. The effects of liquid compressibility on the bubble behavior and impulse pressure were numerically clarified.