Provided is a c-Met inhibitory antitumor agent which mitigates side effects by selectively affecting tumor cells in which c-Met is specifically expressed, having a formula (I) or its salt:wherein each of R1 and R2 are independently a hydrogen atom, an optionally substituted C1-6 alkyl, C3-10 cycloalkyl, C6-14 aromatic hydrocarbon, or saturated or unsaturated heterocyclic group, or R1 and R2 may form, together with the nitrogen atom to which they are attached, an optionally substituted nitrogen-containing heterocyclic ring； R3 is a C1-6 alkyl group； and R4, R5, and R6, are independently a hydrogen atom, a halogen atom, an optionally substituted C1-6 alkyl group, a C1-6 alkoxy group, a C1-6 alkylamino group, an optionally substituted aromatic hydrocarbon group, or an optionally substituted saturated or unsaturated heterocyclic group, or R5 and R6 may form a ring together with the phenyl ring to which they are attached.
