A straddled vehicle comprising: a rear wheel, a prime mover that is configured to rotate the rear wheel, a rear axle shaft that rotatably supports the rear wheel, a swingarm that includes a main arm supporting the rear axle shaft and a bracket protruding upward from the main arm, a supported body mounted on the bracket, a drive chain that is configured to transmit rotation of the prime mover to the rear wheel, a chain adjuster that is configured to adjust tension of the drive chain by moving the rear axle shaft in a front-rear direction of the straddled vehicle with respect to the swingarm among a plurality of positions including an overlapping position and a non-overlapping position, a rear brake that is configured to apply damping force to the rear wheel, an ABS which includes a rotor that is configured to rotate together with the rear wheel and a wheel speed sensor that is configured to detect a rotational speed of the rear wheel by detecting the rotational speed of the rotor, and which is configured to change the damping force of the rear brake based on the rotational speed of the rear wheel, a holder that is configured to hold the wheel speed sensor, is mounted on the rear axle shaft, and that is configured to move in the front-rear direction of the straddled vehicle with respect to the swingarm together with the rear axle shaft, and a sensor fastening member (B2, N1) that includes a tool-fitted portion (B2o, B2c, N1o) disposed on the outer side of the wheel speed sensor in a width direction of the straddled vehicle and configured to come into contact with a tool that is configured to fasten the wheel speed sensor to the holder, characterized in that when the rear axle shaft is at the overlapping position, the bracket of the swingarm overlaps with at least a portion of the tool-fitted portion (B2o, B2c, N1o) of the sensor fastening member (B2, N1) in a side view of the straddled vehicle, and when the rear axle shaft is at the non-overlapping position, the bracket of the swingarm does not overlap with any portion of the tool-fitted portion (B2o, B2c, N1o) of the sensor fastening member (B2, N1) in a side view of the straddled vehicle. a rear wheel, a prime mover that is configured to rotate the rear wheel, a rear axle shaft that rotatably supports the rear wheel, a swingarm that includes a main arm supporting the rear axle shaft and a bracket protruding upward from the main arm, a supported body mounted on the bracket, a drive chain that is configured to transmit rotation of the prime mover to the rear wheel, a chain adjuster that is configured to adjust tension of the drive chain by moving the rear axle shaft in a front-rear direction of the straddled vehicle with respect to the swingarm among a plurality of positions including an overlapping position and a non-overlapping position, a rear brake that is configured to apply damping force to the rear wheel, an ABS which includes a rotor that is configured to rotate together with the rear wheel and a wheel speed sensor that is configured to detect a rotational speed of the rear wheel by detecting the rotational speed of the rotor, and which is configured to change the damping force of the rear brake based on the rotational speed of the rear wheel, a holder that is configured to hold the wheel speed sensor, is mounted on the rear axle shaft, and that is configured to move in the front-rear direction of the straddled vehicle with respect to the swingarm together with the rear axle shaft, and a sensor fastening member (B2, N1) that includes a tool-fitted portion (B2o, B2c, N1o) disposed on the outer side of the wheel speed sensor in a width direction of the straddled vehicle and configured to come into contact with a tool that is configured to fasten the wheel speed sensor to the holder, characterized in that when the rear axle shaft is at the overlapping position, the bracket of the swingarm overlaps with at least a portion of the tool-fitted portion (B2o, B2c, N1o) of the sensor fastening member (B2, N1) in a side view of the straddled vehicle, and when the rear axle shaft is at the non-overlapping position, the bracket of the swingarm does not overlap with any portion of the tool-fitted portion (B2o, B2c, N1o) of the sensor fastening member (B2, N1) in a side view of the straddled vehicle.