A securing device having a radial pin which is inserted into a through-hole having an outside hole and an inside hole and penetrating an outside member in the radial direction of a rotary machine, the outside hole being open to the outside of the outside member in the radial direction of the rotary machine, the inside hole communicating with the outside hole, having a smaller diameter than the outside hole, and being open to the inside in the radial direction of the rotary machine, the radial pin having a portion on the inside in the radial direction of the rotary machine inserted into a recess formed in an inside member, and including a flange portion having an outer diameter larger than a diameter of the inside hole; and a pin support unit which is inserted into the outside hole on the outside in the radial direction of the rotary machine.