There is provided an air mat device comprising a mat unit that has an air cell; an air supply and exhaust unit that supplies air to the air cell and exhausts the air from the air cell; and a control unit that acquires a state change quantity of the air cell or a time required for a state change of the air cell, as a control reference value, and that controls the air supply and exhaust unit in accordance with the control reference value. There is also provided an internal pressure control method of an air cell according to the above configuration.