It is intended to provide a novel compound havinghigh antitumor activity and low toxicity to normal cells.The present invention provides a pyridone carboxylic acidderivative represented by the following formula (1) or asalt thereof wherein R1 represents a hydrogen atom, ahalogen atom or the like； R2 represents a hydrogen atom,a halogen atom or the like； R3 to R6 each represent ahydrogen atom or the like； R7 represents a hydrogen atomor the like； R8 represents a hydrogen atom, a halogenatom, the following formula (a) (wherein Ra1 and Ra2 eachrepresent a hydrogen atom, a hydroxy group, an optionallysubstituted lower alkyl group or the like) or the like,or R7 and R8 together represent =N-OR10 (wherein R10represents a hydrogen atom, an optionally substitutedlower alkyl group, or an aralkyl group), or R7 and R8form an optionally substituted 4- to 6-membered saturatedhetero ring together with the adjacent carbon atom, orthe like； R9 represents a hydrogen atom or the like； Xrepresents a nitrogen atom or the like； and Y representsa nitrogen atom or the like.
