According to embodiments, an air mattress includes an air cell unit including an air cell, and a controller that controls an internal pressure in the air cell. The controller conducts a first operation when the internal pressure in the air cell satisfies the second condition after having satisfied a first condition. The first condition includes the internal pressure becoming from a first value to a second value lower than the first value, a difference between the first value and the second value being equal to or more than a first threshold, and a change rate relative to time of the internal pressure from the first value to the second value being equal to or more than a second threshold. The second condition includes, after the internal pressure has lowered from the first value to the second value, the internal pressure becoming a third value lower than the second value, and a difference between the second value and the third value being equal to or more than a third threshold. In the first operation, the controller changes the internal pressure toward the second value.