A signal processing device which uses a first signal waveform of ultrasound reflected from an object in a first compressed state and a second signal waveform of ultrasound reflected from the object in a second compressed state and calculates an elasticity of the object affected by a change in a compressed state includes: a phase difference calculation unit which calculates a phase difference component in each time between the first signal waveform and the second signal waveform a correlation calculation unit which calculates an elasticity pertaining to a difference in angular frequencies between the first signal waveform and the second signal waveform and an initial phase difference according to a correlation between the each time and the phase difference component in the each time and an elasticity calculation unit which calculates the elasticity on the basis of the difference in angular frequencies.
