The present invention relates to an anticancer agent having a high safety and a superior anticancer activity, and an anticancer agent containing, as an active ingredient, an aminoacetonitrile compound represented by the formula (I) wherein R1 is a hydrogen atom, an alkyl group and the like, R2, R3, and R4 are the same or different and each is a hydrogen atom, an alkyl group and the like, R5 and R6 are the same or different and each is a hydrogen atom, a halogen atom and the like, m is 0 or 1, R is a halogen atom, a cyano group, a nitro group, a phenyl group optionally substituted by an alkyl group and the like, an alkyl group and the like, Ar1 is a phenyl group, a naphthyl group, a pyridyl group, a pyrazolyl group, or the like, each of which is optionally substituted by a halogen atom, a cyano group, a nitro group, alkyl group and the like, and W is —O—, —S—, —SO2—, or —N(R7)— wherein R7 is a hydrogen atom, a (C1-C6)alkyl group and the like, or a pharmacologically acceptable salt thereof.