A rotation-force adjusting device for a toy gun has a pressing tube, an adjusting unit, and a gun body. The pressing tube has a pressing block, a cushion hole, and an abutting portion. The pressing block is formed on and protrudes radially inward from a top portion of the inner surface of the pressing tube. The cushion hole is formed through the top portion of the pressing tube. The abutting portion is formed at the top portion of the pressing tube and is formed on the pressing tube above the cushion hole. The adjusting unit is mounted around the pressing tube and has a force ring and a control knob. The force ring is mounted around the pressing tube, and the control knob is mounted through the force ring. The gun body has an inner barrel mounted through the pressing tube.