Abstract: First and second air cell units 2 and 3, respectively, are divided into their right and left air cells 2a, 3a, 2b and 3b, respectively, and central bent sections 2c and 3c. Each of the bent section 2c and 3c connects associated right and left air cells together at offset relationship in the direction of the mat length. The first and the second air cell units are alternately inflated and deflated, so that the air cells are inflated asymmetrically to thereby support a patient lying thereon at asymmetrical portions. The bent sections 2c and 3c are configured to gently deform the respective air cells so as to allow the bent sections to abut closely on the patient's back without a sense of incompatibility with the air cells. The air mat may thus provide well-balanced and well-distributed supporting forces for the patient, which is suitable for preventing decubitus of the patient.