A nonlinear magnetotransport was studied in the magnetic field induced spin density wave (FISDW) state of (TMTSF)2C104 at temperatures between 0.3K and 4.2K. Non-Ohmic magnetoresistance was observed at plural FISDW sub-phases. The nonlinearity seems to appear only in the diagonal conductivity with a very small threshold electric field. As an origin of this non-Ohmic conduction, the possibility of the sliding motion of SDW is discussed. © 1989.