To provide a sludge treatment apparatus and a sludge treatment method, capable of surely destroying sludge cells, sufficiently reducing the volume of the sludge and easily dehydrating it.

After dissolving a gas in slurry-like sludge under a pressurizing condition by a gas dissolving means 13, the slurry-like sludge is crushed under a pressure lower than the pressure under the pressurizing condition by a destroying means 14. Thus, the gas dissolved inside the sludge cells is turned to bubbles by a pressure difference (the pressure difference between the pressure under the pressurizing condition and the pressure lower than the pressure under the pressurizing condition), the sludge cells are turned to an expanded state and crushed in the expanded state or in the state of getting expanded with the little elastic force of a cell wall (the state that the cell wall is expanded tight), and the sludge cells are surely destroyed.