A rack bar support device supports a rack bar of a steering device of a vehicle toward a pinion shaft, and includes a rack bearing which is disposed opposite the pinion to contact the rack bar and a biasing assembly providing a force of pushing the rack bearing along a biasing axis toward the rack bar to urge the rack bearing to push the rack bar is engaged with the pinion shaft. The biasing assembly includes an adjustment plug, an adjustment assembly and a support plate assembly. The support plate assembly includes a support plate which is movably disposed between the adjustment member and the rack bearing in a state of being supported by the adjustment member, and a gap is formed between the support plate and the rack bearing.