Provided is a compound that is useful as a prophylactic and/or therapeutic agent for bladder cancer. The inventors studied compounds having FGFR-inhibiting activity and completed the present invention upon confirming that the nitrogen-containing aromatic heterocyclic compound of the present invention has FGFR1-, 2-, and/or 3-inhibiting activity, particularly mutant FGFR3-inhibiting activity. This nitrogen-containing aromatic heterocyclic compound can be used as a therapeutic agent for a variety of cancers in which FGFR1, 2 and/or 3 play a role, such as lung cancer and hormone therapy-resistant breast cancer, stomach cancer, triple-negative breast cancer, uterine cancer, bladder cancer, and glioblastoma, particularly as a prophylactic and/or therapeutic agent for mutant FGFR3-positive bladder cancer.