A novel compound having high antitumor activity and low toxicity to normal cells is provided.The following formula (1):In Formula 1, R1 is hydrogen atom, halogen atom, etc. R2 is hydrogen atom, halogen atom, R3 to R6 is hydrogen atom; R7 is hydrogen atom; R8 is hydrogen atom, halogen atom, equation (a):(in the equation, ra1 and ra2 are hydrogen atoms, hydroxy groups, lower alkyl groups, etc., which may have substituents), or R7 and R8, where n is 10 or 10, where R10 is a hydrogen atom, a low alkyl group having a substituent or an aryl group.Where R7 and R8 form a group of four to six saturated hetero rings which may be substituted with adjacent carbon atoms, such as hydrogen atom, etc., R9 is hydrogen atom, X is nitrogen atom; y is nitrogen atom, etc.)The pyridone carboxylic acid derivative or salt thereof.抗腫瘍活性が高く、正常細胞への毒性が低い新規化合物を提供する。 下記式(1):〔式中、R1は水素原子、ハロゲン原子等;R2は水素原子、ハロゲン原子等、R3~R6は水素原子等;R7は水素原子等;R8は、水素原子、ハロゲン原子、下記式(a):(式中、Ra1及びRa2は、水素原子、ヒドロキシ基、置換基を有していてもよい低級アルキル基等)等、又は、R7とR8で=N-OR10(ここで、R10は水素原子、置換基を有していてもよい低級アルキル基、又はアラルキル基を示す。)、R7とR8が隣接する炭素原子と一緒になって置換基を有していてもよい4~6員の飽和ヘテロ環を形成等;R9は水素原子等、Xは窒素原子等;Yは窒素原子等。〕で表されるピリドンカルボン酸誘導体又はその塩。