The present invention allows even soft tissue such as body tissue having a hierarchic structure of skin, fat, muscle and bone, etc., to be estimated and allows estimation only through a short-time pressing operation to thereby reduce damages to the soft tissue. The present invention is constructed of an ultrasonic probe for transmitting/receiving an ultrasonic signal, a target deformation amount calculation section for calculating an amount of deformation of a target shape from a time variation of data received from the ultrasonic probe, a movement mechanism for moving the ultrasonic probe, a probe control section for controlling the probe, a position sensor for measuring the position of the probe, a force sensor for measuring a force applied to the probe section, a viscoelasticity estimation section for estimating viscoelasticity of the target based on values obtained from the position sensor, force sensor, target deformation amount calculation section and a viscoelasticity display section for presenting the estimated viscoelasticity to the user.