Provided is a compound useful as a prophylactic and/or therapeutic agent for bladder cancer. As a result of studies on compounds having FGFR inhibitory action, the present inventors have found that the nitrogen-containing aromatic heterocyclic compounds of the present invention have inhibitory action on FGFR1, FGFR2, and/or FGFR3, particularly, mutant FGFR3, and thus, the present invention has been accomplished. The nitrogen-containing aromatic heterocyclic compound of the present invention can be used as a therapeutic agent for various cancers related to FGFR1, FGFR2, and/or FGFR3, such as lung cancer and hormone therapy-resistant breast cancer, stomach cancer, triple negative breast cancer, endometrial cancer, bladder cancer, and glioblastoma, particularly as a prophylactic and/or therapeutic agent for mutant FGFR3-positive bladder cancer.
