Provided is an air mattress configured so that the pressure within each of bladder-shaped cells is variable, wherein the sleeping comfort of a person lying on the air mattress is not reduced.The air mattress has a plurality of air cell groups, each of which constituted by a plurality of bladder-shaped cells and lined up with respect to the lengthwise direction of the air mattress; an air supply/release pump; an air tube linking the bladder-shaped cells and the air supply/release pump in an independent first system for each of the air cell groups and an independent second system for each of specific bladder-shaped cells out of the plurality of air cell groups; and a pressure sensor for measuring the pressure within the bladder-shaped cells for each of the first and second systems. One or a plurality of specific air cell groups is constituted by an upper section, a middle section, and a lower section of bladder-shaped cells lined up in the lengthwise direction of the air mattress; the pressure in the lower section bladder-shaped cells is controlled by the first system and the pressure in the middle section bladder-shaped cells is controlled by the second system; and the upper section bladder-shaped cells communicate with the middle section bladder-shaped cells.