A nematic liquid crystal compound represented by any one of formulas (a-1) to (a-6): ##STR00001## in formulas (a-1) to (a-6), Ra and Rb are each independently hydrogen or alkyl having 1 to 10 carbons, provided that in the alkyl, --CH2- may be replaced by --O--, --(CH2)2- may be replaced by --CH.dbd.CH--, and hydrogen may be replaced by a halogen; ring A1 and ring A2 are each independently trans-1,4-cyclohexylene or 1,4-phenylene, provided that in these rings hydrogen may be replaced by a halogen, and in the case where the ring is trans-1,4-cyclohexylene, --CH2- may be replaced by --O--, and --CH2CH-- may be replaced by --CH.dbd.C--; and Z1 and Z2 are each independently a single bond, --COO--, --OCO--, --OCH2-, --CH2O-- or --CH2CH2-, provided that in formula (a-3), in the case where ring A2 is trans-1,4-cyclohexylene, Z2 is a single bond, --COO--, --OCO--, --OCH2- or --CH2O--, in the case where Ra is --C3H7, Rb is --OC2H5, and Z2 is a single bond, ring A2 is trans-1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2-fluoro-3-chloro-1,4-phenylene, 2-chloro-3-fluoro-1,4-phenylene or 2,3-dichloro-1,4-phenylene, and in formula (a-4), in the case where ring A1 is trans-1,4-cyclohexylene, Z1 is a single bond, --COO--, --OCO--, --OCH2O--.