An ultrasound observation system includes: an ultrasound transducer that transmits ultrasound to a subject and receives ultrasound from the subject and generates an ultrasound signal a displacement measurement circuit for elasticity image generation that measures a displacement of the subject based on the ultrasound signal an elasticity modulus calculation circuit that calculates an elasticity modulus of the subject based on the measured displacement a first automatic pressurization mechanism that generates a pressurization displacement in the subject a signal waveform analysis circuit that analyzes a periodic motion based on a waveform of a signal that is based on a spontaneous displacement of the subject and a pressurization mechanism control circuit that controls the first automatic pressurization mechanism so as to generate a pressurization displacement that reduces an influence of the spontaneous displacement of the subject at a time that an elasticity modulus is calculated based on the signal waveform analysis result.
