Abstract: This invention relates to a malonic acid derivative represented by the general formula (I) ##STR1## wherein R.sup.1 and R.sup.2, which may be the same or different, represents hydrogen atom; C.sub.1 -C.sub.12 alkyl group; C.sub.1 -C.sub.8 alkyl group substituted with C.sub.1 -C.sub.5 alkoxy group, a tetrahydrofuryl group, a phenyl group or a phenyl group substituted with 1 to 3 groups selected from the group consisting of halogen atoms, C.sub.1 -C.sub.5 alkyl groups and C.sub.1 -C.sub.5 alkoxy groups; or C.sub.2 -C.sub.6 alkenyl group; R.sup.3 and R.sup.4, which may be the same or different, represent hydrogen atom, C.sub.1 -C.sub.6 alkyl group, C.sub.2 -C.sub.6 alkenyl group, C.sub.2 -C.sub.8 alkoxyalkyl group, benzoyl group, C.sub.2 -C.sub.8 alkylcarbonyl group, C.sub.2 -C.sub.8 alkoxycarbonyl group, C.sub.1 -C.sub.4 alkylsulfonyl group or aralkyl group including benzyl group, and R.sup.5, R.sup.6 and R.sup.7, which may be the same or different, represent hydrogen atom or C.sub.1 -C.sub.