An air mattress, in which, when used as a mat, an air layer inflated into a sealed space formed by a bilaminar airtight fabrics and a bonding line between the bilaminar airtight fabrics supports a user's weight to provide insulation and cushioning between the user and the floor, and which when not used, is deflated to reduce the volume and is folded for easy handling, the air mattress comprising: thermal fusion lines formed by pressing and thermally fusing a pocket-system air suction/discharge hole, a tube-system suction/discharge hole, and tube members arranged between a lower sheet and an upper sheet; a pocket system, which includes the pocket-system air suction/discharge hole, air pockets, and connection parts between the air pockets bordering the tube members, and serves to support a user's weight; and a tube system, which includes the tube-system suction/discharge hole, the tube members, and communication parts, and serves to block the airflow between the air pockets, wherein when air is first injected into the pocket system, an air flow between the air pockets is allowed into gaps among air communication holes, a mattress member, and the tube members, such that the entire pocket system is filled with air, and when air is injected into the tube system at a higher pressure than the pocket system, the tube members expand to block the gaps among the air communication holes, the mattress member, and the tube members such that the airflow between the air pockets is blocked and the air pockets support the user's weight to alleviate excessive sagging of the part where the user's weight is applied, thereby providing insulation and cushioning between the user and the floor, and allowing the user to more easily move or turn over on the air mattress by reducing the height difference between the part sagged by the user's weight and the part to which the user's weight is not applied and the contact (friction) area between the user and the air mattress. thermal fusion lines formed by pressing and thermally fusing a pocket-system air suction/discharge hole, a tube-system suction/discharge hole, and tube members arranged between a lower sheet and an upper sheet; a pocket system, which includes the pocket-system air suction/discharge hole, air pockets, and connection parts between the air pockets bordering the tube members, and serves to support a user's weight; and a tube system, which includes the tube-system suction/discharge hole, the tube members, and communication parts, and serves to block the airflow between the air pockets, wherein when air is first injected into the pocket system, an air flow between the air pockets is allowed into gaps among air communication holes, a mattress member, and the tube members, such that the entire pocket system is filled with air, and when air is injected into the tube system at a higher pressure than the pocket system, the tube members expand to block the gaps among the air communication holes, the mattress member, and the tube members such that the airflow between the air pockets is blocked and the air pockets support the user's weight to alleviate excessive sagging of the part where the user's weight is applied, thereby providing insulation and cushioning between the user and the floor, and allowing the user to more easily move or turn over on the air mattress by reducing the height difference between the part sagged by the user's weight and the part to which the user's weight is not applied and the contact (friction) area between the user and the air mattress.