Resistivity measurements were performed on (TMTTF) 2 Br under pressure. Magnetic field was applied along c * -axis up to 16T. Above 0.5GPa, (TMTTF) 2 Br exhibits incommensurate spin density wave (ISDW) transition at low temperature. With increasing pressure, spin density wave (SDW) transition temperature T S D W decreases from 19.5K at 0.5GPa to 12.5K at 2.1GPa. In the incommensurate SDW phase, with increasing magnetic field, T S D W increases quadratically and the coefficient of quadratic term increases with increasing pressure. These results are qualitatively consistent with the prediction of the mean-field theory based on the imperfection of the nesting of Fermi surface. The relation between the coefficient of the quadratic term and T S D W at zero magnetic field can be explained by the mean-field theory with taking into account the reduction of the coupling constant N(0)I by pressure.