A tapping screw fastening jig that fastens a fastening tool using a tapping screw to a mating member having at least three non-threaded pilot holes, the tapping screw fastening jig comprising: a guide component; and a positioning component, wherein: the guide component includes a first base member provided with a guide hole portion through which the tapping screw is insertable at a position corresponding to each of the pilot holes in a use state of the tapping screw fastening jig; and the positioning component includes: a second base member; and at least two positioning pins (P10, P20) provided on the second base member, where the at least two positioning pins (P10, P20) are provided at positions corresponding to at least two of the pilot holes in the use state, wherein each of the at least two positioning pins (P10, P20) including a first outer diameter portion (P11, P21) that is insertable into the pilot hole in the use state, and a second outer diameter portion (P12, P22) that is connected to the first outer diameter portion (P11, P21) on a base end side of the first outer diameter portion (P11, P21) and is insertable through the guide hole portion in the use state. a guide component; and a positioning component, wherein: the guide component includes a first base member provided with a guide hole portion through which the tapping screw is insertable at a position corresponding to each of the pilot holes in a use state of the tapping screw fastening jig; and the positioning component includes: a second base member; and at least two positioning pins (P10, P20) provided on the second base member, where the at least two positioning pins (P10, P20) are provided at positions corresponding to at least two of the pilot holes in the use state, wherein each of the at least two positioning pins (P10, P20) including a first outer diameter portion (P11, P21) that is insertable into the pilot hole in the use state, and a second outer diameter portion (P12, P22) that is connected to the first outer diameter portion (P11, P21) on a base end side of the first outer diameter portion (P11, P21) and is insertable through the guide hole portion in the use state. the guide component includes a first base member provided with a guide hole portion through which the tapping screw is insertable at a position corresponding to each of the pilot holes in a use state of the tapping screw fastening jig; and the positioning component includes: a second base member; and at least two positioning pins (P10, P20) provided on the second base member, where the at least two positioning pins (P10, P20) are provided at positions corresponding to at least two of the pilot holes in the use state, wherein each of the at least two positioning pins (P10, P20) including a first outer diameter portion (P11, P21) that is insertable into the pilot hole in the use state, and a second outer diameter portion (P12, P22) that is connected to the first outer diameter portion (P11, P21) on a base end side of the first outer diameter portion (P11, P21) and is insertable through the guide hole portion in the use state. a second base member; and at least two positioning pins (P10, P20) provided on the second base member, where the at least two positioning pins (P10, P20) are provided at positions corresponding to at least two of the pilot holes in the use state, wherein each of the at least two positioning pins (P10, P20) including a first outer diameter portion (P11, P21) that is insertable into the pilot hole in the use state, and a second outer diameter portion (P12, P22) that is connected to the first outer diameter portion (P11, P21) on a base end side of the first outer diameter portion (P11, P21) and is insertable through the guide hole portion in the use state.