and the second and third links 62 63 integrally assembled by the first and second connecting shafts 71 72 are rotated at a phase difference of 180 degrees fig4 b illustrates the links 61 62 63 having been rotated by 90 degrees in a counterclockwise direction around the third connecting shaft 73 from the fig4 a position that is as the links 61 62 63 are rotated in the housing 80 respective side surfaces 51s 52s of thrusters 51 52 contact respective side walls 81s 82s of openings 81 82 thus the thrusters 51 52 are moved outward to the exterior of the housing 80 subsequently as the links 61 62 63 continue to be rotated in a counterclockwise direction around the third connecting shaft 73 from the position of fig4 b to the position of fig4 c or 3b the first and second thrusters 51 52 are extended at a maximum distance toward the vertical wall of the spin barrel 12 next when the links 61 62 63 are further rotated in a counterclockwise direction around the third connecting shaft 73 respective side surfaces 51t 52t of respective thrusters 51 52 contact respective side walls 81t 82t of respective openings 81 82 as.