An ultrasound diagnostic device 101 is equipped with a probe distance determiner 7 and a screen creator 8. The probe distance determiner 7 analyses a positional relationship between a probe and an area subject to measurement appearing in an ultrasound image, and determines whether or not the analysed positional relationship is appropriate. The screen creator 8 notifies a user of determination results. An appropriate positional relationship is one in which a pixel region having luminance characteristics of a gelatinous medium is present between an element array of an ultrasound probe 102 and the area subject to measurement appearing in the ultrasound image, and in which the distance between the prove and the area subject to measurement exceeds a predetermined threshold across the entire length of the element array.