Liquid crystal composition and liquid crystal display device

A liquid crystal composition that has a positive dielectric anisotropy and a nematic phase, and contains at least one compound selected from the group of compounds represented by formula (1) as an additive component and at least one compound from the group of compounds represented by formula (2) as a first component:

• wherein, in formula (1), R1 is hydrogen or alkyl having 1 to 15 carbons;
• R2, R3, R4 and R5 are independently hydrogen or alkyl having 1 to 4 carbons;
• ring A is a polyvalent group derived from benzene or cyclohexane by eliminating hydrogen;
• a is 3 or 4;
• and
• in formula (2), R6 is alkyl having 1 to 12 carbons, alkoxy having to 12 carbons or alkenyl having 2 to 12 carbons;
• ring B is 1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl;
• Z1 is a single bond, ethylene, carbonyloxy or difluoromethyleneoxy;
• X1 and X2 are independently hydrogen or fluorine;
• Y1 is fluorine, chlorine, alkyl having 1 to 12 carbons in which at least one of hydrogen is replaced by fluorine or chlorine, alkoxy having 1 to 12 carbons in which at least one of hydrogen is replaced by fluorine or chlorine, or alkenyloxy having 2 to 12 carbons in which at least one of hydrogen is replaced by fluorine or chlorine;
• and b is 1, 2, 3 or 4.