A wire harness installation structure comprising: a wire harness having bend flexibility; a protector configured to protect the wire harness while allowing the wire harness to make a bending movement about a bending position of the wire harness, the bending position being located between both ends of the wire harness; and a bending motion mechanism that causes the wire harness to make the bending movement, wherein: the wire harness has a first portion that is fixed to the protector, a second portion that is distant from both of the first portion and the protector beyond the bending position, and a third portion that is located between the first portion and the second portion, and the third portion is offset in a direction of the bending movement from an imaginary straight line connecting the first portion and the second portion; and the second portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism; characterized in that: the third portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism and the wire harness is routed so that a second excess length between the second portion and the third portion is shorter than a first excess length between the first portion and the third portion. a wire harness having bend flexibility; a protector configured to protect the wire harness while allowing the wire harness to make a bending movement about a bending position of the wire harness, the bending position being located between both ends of the wire harness; and a bending motion mechanism that causes the wire harness to make the bending movement, wherein: the wire harness has a first portion that is fixed to the protector, a second portion that is distant from both of the first portion and the protector beyond the bending position, and a third portion that is located between the first portion and the second portion, and the third portion is offset in a direction of the bending movement from an imaginary straight line connecting the first portion and the second portion; and the second portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism; characterized in that: the third portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism and the wire harness is routed so that a second excess length between the second portion and the third portion is shorter than a first excess length between the first portion and the third portion. the wire harness has a first portion that is fixed to the protector, a second portion that is distant from both of the first portion and the protector beyond the bending position, and a third portion that is located between the first portion and the second portion, and the third portion is offset in a direction of the bending movement from an imaginary straight line connecting the first portion and the second portion; and the second portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism; characterized in that: the third portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism and the wire harness is routed so that a second excess length between the second portion and the third portion is shorter than a first excess length between the first portion and the third portion. the third portion of the wire harness is fixed on a movable member (20, 21) of the bending motion mechanism and the wire harness is routed so that a second excess length between the second portion and the third portion is shorter than a first excess length between the first portion and the third portion.