A pressure tank including, a tank wall; a supporting member which includes fiber reinforced plastic and supports an outer surface of the tank wall; a supersonic wave sensor which is connected to the tank wall, and which detects a sonic wave propagated in the tank wall; and an internal abnormality determination member which is connected to the supersonic wave sensor, and which determines whether an internal abnormality exits in the tank wall, wherein the internal abnormality determination member determines the existence of the internal abnormality based on the detection result during gas is charged into the pressure tank, and outputs an abnormality signal when the internal abnormality was determined to exist.