A flat cable that includes a plurality of conductors respectively extending in an axial direction; and an insulating sheath configured to, in a state where the conductors are lined up in a width direction orthogonal to the axial direction of the conductors, restrict the conductors from outside and collectively cover the conductors, wherein the insulating sheath has an expander enabling bending in the width direction by permitting relative displacement between the conductors, and the expander, by expanding so as to partially separate from the conductors in at least a thickness direction orthogonal to both the width direction and the axial direction, forms an internal space permitting relative displacement such that adjacent conductors overlap in the thickness direction.