A vessel wall monitoring apparatus includes: a first detecting unit which detects vessel diameter information based on first biological information obtained from a subject; a first producing unit which differentiates the vessel diameter information detected by the first detecting unit, to produce a vessel diameter function; a second detecting unit which detects blood pressure based on second biological information obtained from the subject; a second producing unit which performs a logarithmic operation on the blood pressure detected by the second detecting unit, to produce a logarithmic blood pressure function; and an outputting unit which produces an impedance model expression by using the vessel diameter function, the logarithmic blood pressure function, and mechanical characteristic values including a stiffness, viscosity, and inertia, and which calculates and outputs at least one of the stiffness, the viscosity, and the inertia based on the impedance model expression.