  We present the results of a ^{1}H NMR study of the single-component molecular
conductor, [Au(tmdt)_{2}].
  A steep increase in the NMR line width and a peak formation of the nuclear
spin-lattice relaxation rate, 1/T_{1}, were observed at around 110 K.
  This behavior provides clear and microscopic evidences for a magnetic phase
transition at considerably high temperature among organic conductors.
  The observed variation in 1/T_{1} with respect to temperature indicates the
highly correlated nature of the metallic phase.
