A wiring harness guiding apparatus guiding a wiring harness between a car body and a slide body supported by a support body arranged slidably at a long-pipe-shaped rail fixed at the car body, comprising: the long-pipe-shaped rail fixed at the car body; the support body supporting the slide body and arranged slidably at the long-pipe-shaped rail; and a protector having: a wiring harness fixing member fixing the wiring harness led from an opening arranged at one end along a lengthwise direction of the rail into the rail; and a lead-out member extending with a pipe shape from the wiring harness fixing member so as to pass through a slit arranged between one end and the other end of the rail provided along a lengthwise direction of the rail to an outside of the rail, and leading the wiring harness therethrough toward the slide body; characterized in that the protector includes a support body mount member which engages with a mounted member of the support body, and the support body mount member extends with a plate shape from one end of the wiring harness fixing member and includes a hole positioning the mounted member inside thereof and the support body mount member has a clearance between the support body mount member and the mounted member so that the support body mount member to be movable along a widthwise direction of the rail. the long-pipe-shaped rail fixed at the car body; the support body supporting the slide body and arranged slidably at the long-pipe-shaped rail; and a protector having: a wiring harness fixing member fixing the wiring harness led from an opening arranged at one end along a lengthwise direction of the rail into the rail; and a lead-out member extending with a pipe shape from the wiring harness fixing member so as to pass through a slit arranged between one end and the other end of the rail provided along a lengthwise direction of the rail to an outside of the rail, and leading the wiring harness therethrough toward the slide body; a wiring harness fixing member fixing the wiring harness led from an opening arranged at one end along a lengthwise direction of the rail into the rail; and a lead-out member extending with a pipe shape from the wiring harness fixing member so as to pass through a slit arranged between one end and the other end of the rail provided along a lengthwise direction of the rail to an outside of the rail, and leading the wiring harness therethrough toward the slide body; the protector includes a support body mount member which engages with a mounted member of the support body, and the support body mount member extends with a plate shape from one end of the wiring harness fixing member and includes a hole positioning the mounted member inside thereof and the support body mount member has a clearance between the support body mount member and the mounted member so that the support body mount member to be movable along a widthwise direction of the rail. a support body mount member which engages with a mounted member of the support body, and the support body mount member extends with a plate shape from one end of the wiring harness fixing member and includes a hole positioning the mounted member inside thereof and the support body mount member has a clearance between the support body mount member and the mounted member so that the support body mount member to be movable along a widthwise direction of the rail.