To improve the strength of the whole flexible shaft coupling against torque by arranging a plate spring made of a material with a large elastic modulus at the center section in the overlapping direction between multiple plate springs, and arranging the plate springs made of a material with an elastic modulus smaller than the elastic modulus of the plate spring of the center section on the outside.

A plate spring 8 made of a material with a large elastic modulus is arranged between two plate springs 7a, 7b, and the plate springs 7a, 7b made of a material with an elastic modulus smaller than the elastic modulus of the material of the plate spring 8 of the center section are arranged on the outside, or a plate spring 9 made of a metal material with a large elastic modulus and plate springs 10a, 10b made of a nonmetalic material with a small elastic modulus are arranged, or a plate spring 11 using steel or titanium as a metal material and plate springs 12a, 12b using CFRP as a nonmetalic material are arranged, or a plate spring 13 using CFRP as a material with a large elastic modulus and plate springs 14a, 14b using GFRP as a material with a small elastic modulus are arranged, or a plate spring 15 using steel as a material with a large elastic modulus and plate springs 16a, 16b using titanium as a material with a small elastic modulus are arranged.