An ultrasound observation apparatus according to the present invention is configured to generate a combined image by combining a plurality of ultrasound images generated based on an echo signal being an electrical signal converted from an ultrasound echo being ultrasound that is transmitted to an observation target and reflected from the observation target. The ultrasound observation apparatus includes a frame memory, a frame memory correlation unit, a frame memory position correction unit, and a weighting and adding unit. The frame memory stores the plurality of ultrasound images in chronological order. The frame memory correlation unit detects a moving amount and a moving direction, as three-dimensional correlation, of the ultrasound image of a past frame with respect to the ultrasound image of a latest frame, among the plurality of ultrasound images stored in the frame memory. The frame memory position correction unit moves a relative position of the ultrasound image of the past frame based on the three-dimensional moving amount and moving direction. The weighting and adding unit performs weighting processing on the ultrasound image of the past frame based on the three-dimensional moving amount.
