This ultrasound image generating device comprises an ultrasound probe which transmits ultrasound into a subject, receives reflected sound, and outputs an ultrasound detection signal, said ultrasound image generating device generating a topographical image which represents a shape. The ultrasound image generating device further comprises: a sound speed value computation unit which computes a sound speed value in a region of interest in the topographical image and a degree of reliability information generation unit which generates degree of reliability information of the sound speed value on the basis of the sound speed value corresponding to the region of interest.
