Assembling structure of support device of a chair

A support device of a chair, comprising:

• an outer frame, having a surrounding trough;
• fasteners, disposed in the surrounding trough, and each having an engaging portion;
• an inner frame, having a front and a rear;
• a supporting body, made of a flexible material, and having a loading side and a connecting side;
• and
• pressing strips, surroundingly attached on a periphery of the connecting side, and an interval being kept between two adjacent pressing strips to provide flexibility;
• wherein the supporting body covers the front of the inner frame, the pressing strips are fastened onto the rear of the inner frame, the inner frame with the supporting body is embedded into the surrounding trough to engage with the engaging portions of the fasteners, the inner frame is formed with installing holes corresponding to the engaging portions of the fasteners, an inner wall of each installing hole is provided with a protrudent step portion and a inserting hole formed in the step portion, the engaging portion is composed of elastic arms arranged in an umbrella shape, an outer diameter of the engaging portion is greater than an inner diameter of the inserting hole, so that when the engaging portion has passed the inserting hole, and the elastic arms restore to engage with the step portion.