A chair-like exercising apparatus comprises a back, a seat, front legs, rear legs, and resistance element(s) which provide a broad range of resistance force adjustable by the user for the back extension exercise. The chair back pivotally connects to the rear legs directly, and pivotally connects to the front legs or rear legs through the resistance element(s). The resistance element comprises a compress-coil-spring cylinders (or constant-force-spring devices) and the cylinder holders (or the device holders). The resistance level of the back extension exercise is adjusted by switching the interchangeable compress-coil-spring cylinders (or constant-force-spring devices) of appropriate loads inside the cylinder holders (or device holders). A user sits on the chair and sway backward to perform back extension exercise after selecting an appropriate resistance level based on his/her physical condition. The apparatus is simple, affordable and can be used as a regular chair in its locked position. A regular back extension exercise with proper resistance force strengthens the low back muscles (erector spinae), improves and prevents the low back pain symptoms.