A material hardness distribution display system (10) includes a probe unit (20) in which a plurality of probe elements (22) are two-dimensionally arranged. Each of the probe elements (22) has an oscillator (26) for introducing oscillation into a biological tissue and an oscillation detection sensor (28) which detects a reflected wave. The probe elements (22) are successively selected by a switch circuit (50) and connected to a hardness calculation unit (70) and a measurement depth calculation unit (82). The hardness calculation unit (70) executes a frequency component analysis for an incident wave signal to the oscillator (26) and a reflected wave signal from the oscillation detection sensor (28) to calculate the hardness of the biological tissue on the basis of the analysis results. The measurement depth calculation unit (82) calculates a measurement depth inside the biological tissue at a position where the hardness has been measured, on the basis of a temporal position of the incident wave signal and a temporal position of the reflected wave signal. They are correlated to the respective probe elements (22).