[Problem] A method for measuring a viscoelastic modulus of a substance and an apparatus for measuring the viscoelastic modulus of the substance are provided for allowing information on viscoelasticity of an adsorption substance to be expressed by moduli G′ and G″ which are generally used when expressing viscoelasticity, and for further allowing calculation of the viscoelastic modulus in real time.[Solution] In a system for forming a film by adsorbing a substance to the surface of a piezoelectric element or to a film fixed onto the piezoelectric element in a solution, at least two of N-th waves of the piezoelectric element are used, and at least two of a resonance frequency Fs, and half-value frequencies F1 and F2 (F2>F1) having half conductance values of a conductance value of the resonance frequency in each N-th wave are used to calculate a mass load term, a viscoelastic term (1), a viscoelastic term (2), and a viscoelastic term (3), and to calculate viscoelastic moduli G′ (storage elastic modulus) and G″ (loss elastic modulus) of the film.