A mattress comprising: a plurality of cells (14a, 14b, 14c); characterized by pressure sensors (150a, 150b, 150c) for detecting the internal pressure of the cells (14a, 14b, 14c); a pump connected to adjust the amount of air in each cell (14a, 14b, 14c); communication paths (42, 44) from the pump to the plurality of cells (14a, 14b, 14c); selector valves (60a, 62a, 60b, 62b, 60c, 62c, 64), arranged on the communication paths (42, 44) between each of the cells (14a, 14b, 14c) and the pump, and capable of switching between, at least, a state for creating communication between the cell (14a, 14b, 14c) and the pump and a state for opening the cell (14a, 14b, 14c) to atmospheric pressure; and, a calibration means (100, 120, 160, 170) for calibrating the pressure sensors (150a, 150b, 150c), the calibration means (100, 120, 160, 170) comprising: a calibration determining means (100, 120) that adopts one cell as a calibration standard cell, determines whether a pressure detected by a pressure sensor connected to the calibration standard cell has continuously fallen within a regulated pressure range at calibration for a regulated duration at calibration when a selector valve (60c, 62c) connected to the calibration standard cell is opened to atmospheric pressure; a first calibration means (100, 120) that, when the pressure detected by the pressure sensor connected to the calibration standard cell has continuously fallen within the regulated pressure range at calibration for the regulated duration at calibration, performs zero-point adjustment of the pressure sensor connected to the calibration standard cell, based on a pressure value detected by the pressure sensor; an internal pressure adjustment means (100, 160, 170) that creates communication between the plurality of cells (14a, 14b, 14c) to perform internal pressure adjustment of the plurality of cells (14a, 14b, 14c) to a predetermined internal pressure value, based on the a pressure value detected by the pressure sensor connected to the calibration standard cell; and, a second calibration means that calibrates each of the pressure sensors (150a, 150b, 150c) connected to the plurality of cells (14a, 14b, 14c) to the pressure value of the pressure sensor belonging to the calibration standard cell, the pressure value being based on the internal pressure adjusted by the internal pressure adjustment means (100, 160, 170). a plurality of cells (14a, 14b, 14c); pressure sensors (150a, 150b, 150c) for detecting the internal pressure of the cells (14a, 14b, 14c); a pump connected to adjust the amount of air in each cell (14a, 14b, 14c); communication paths (42, 44) from the pump to the plurality of cells (14a, 14b, 14c); selector valves (60a, 62a, 60b, 62b, 60c, 62c, 64), arranged on the communication paths (42, 44) between each of the cells (14a, 14b, 14c) and the pump, and capable of switching between, at least, a state for creating communication between the cell (14a, 14b, 14c) and the pump and a state for opening the cell (14a, 14b, 14c) to atmospheric pressure; and, a calibration determining means (100, 120) that adopts one cell as a calibration standard cell, determines whether a pressure detected by a pressure sensor connected to the calibration standard cell has continuously fallen within a regulated pressure range at calibration for a regulated duration at calibration when a selector valve (60c, 62c) connected to the calibration standard cell is opened to atmospheric pressure; a first calibration means (100, 120) that, when the pressure detected by the pressure sensor connected to the calibration standard cell has continuously fallen within the regulated pressure range at calibration for the regulated duration at calibration, performs zero-point adjustment of the pressure sensor connected to the calibration standard cell, based on a pressure value detected by the pressure sensor; an internal pressure adjustment means (100, 160, 170) that creates communication between the plurality of cells (14a, 14b, 14c) to perform internal pressure adjustment of the plurality of cells (14a, 14b, 14c) to a predetermined internal pressure value, based on the a pressure value detected by the pressure sensor connected to the calibration standard cell; and, a second calibration means that calibrates each of the pressure sensors (150a, 150b, 150c) connected to the plurality of cells (14a, 14b, 14c) to the pressure value of the pressure sensor belonging to the calibration standard cell, the pressure value being based on the internal pressure adjusted by the internal pressure adjustment means (100, 160, 170).