Field-induced transitions were studied in Mn3GaC in magnetic fields up to 370 kOe. The antiferromagnetic (AFM)-ferromagnetic (FM) field-induced transition is of the first order. The saturation magnetization σs at 4.2 K in the FM state is 75.0 emu g-1 equivalent to 1.1 μB per Mn atom. The decreasing rate of σs is rather smaller than that of the S = 1/2 Brillouin function. In the magnetostriction measurement of Mn3GaC, an abrupt volume contraction of -0.50% was found at the AFM-FM transition temperature. The result of the forced volume magnetostriction measurement shows that σs at 4.2 K increases with pressure.