In a process of varying pressure of a pressure container (24) accommodating a forearm (22) of a subject (20) in a pressure range including negative pressure, a diameter (cross-sectional shape value) (D) of an artery 44 in the forearm (22) accommodated in the pressure container (24) is measured non-invasively by a vascular diameter calculating unit (76). In addition, a display controller (display controlling means) (80) operates to display on a displaying device (16) a variation of an internal pressure (Pc) in the pressure container (24) and a variation of the diameter (D) of the artery (44) varying depending thereon. Based on the diameter (D) of the artery (44) obtained in the high pressure region, the variation of the internal pressure Pc in the pressure container 24 and the variation of the diameter (D) of the artery 44 varying depending thereon i.e. mechanical properties of the artery (44) are displayed on the displaying device (16). The artery (44) can be evaluated accurately based on the mechanical properties.