NOVEL COMPOUNDS OR SALTS THEREOF, OR CRYSTALS THEREOF, ARE PROVIDED WHICH INHIBIT AXL AND ARE USEFUL FOR TREATING DISEASES CAUSED BY AXL HYPERFUNCTION, DISEASES ASSOCIATED WITH AXL HYPERFUNCTION AND/OR DISEASES ACCOMPANIED BY AXL HYPERFUNCTION. PYRIDONE DERIVATIVES REPRESENTED BY FORMULA (1) HAVING VARIOUS SUBSTITUENTS OR SALTS THEREOF, OR CRYSTALS THEREOF (WHERE R1, R2, R3, R5, R6, A, W, X AND N IN THE FORMULA (1) ARE AS DEFINED IN THE SPECIFICATION, RESPECTIVELY) ARE PROVIDED.