Utlrasound observation apparatus and operation method of ultrasound observation apparatus

An ultrasound observation apparatus configured to cause a display to display an ultrasound image that is generated based on an ultrasound signal that is received from an ultrasound transducer configured to transmit ultrasound to a subject to be observed and receive the ultrasound that is reflected from the subject to be observed, the ultrasound observation apparatus comprising:

• an operation controller configured to control a shape of a region of interest that is set in the ultrasound image according to a change in a contact position at which a contacting object contacts a touch pad, the operation controller being configured to
• detect two contact positions of the contacting object on the touch pad,
• calculate a first positional relationship based on the two contact positions in the touch pad,
• detect a position of the region of interest that is set in the ultrasound image,
• calculate a second positional relationship based on a position at which the region of interest is set and on a reference position, and
• control the shape of the region of interest based on a relative relationship between the first positional relationship and the second positional relationship.