Abstract: A coil spring includes a wire rod including a round section portion and a flat section portion. The round section portion includes a first cross section whose cross section is round. The flat section portion includes a second cross section that is flat. The second cross section has a width greater than or equal to the diameter of the first cross section and a thickness less than the width. A polar moment of inertia of area of the second cross section is smaller than that of the first cross section. A variable section portion is formed between the round section portion and the flat section portion. The variable section portion changes its cross section from circular to flat from the round section portion towards the flat section portion.

Abstract: A Czochralski-type single crystal pulling apparatus in which the heater device is adapted to shift vertically, and a control device is provided for controlling the vertical shifting of the heater and the crucible assembly in predetermined manners, of which a preferred manner is to control the vertical shifting of the heater and the crucible assembly such that the vertical velocities of the crucible assembly and the heater are in direct proportion to the vertical velocity of the pull means.