The present invention provides novel compounds having a P2X 3 and/or P2X 2/3 receptor antagonistic activity. A compound of Formula (I): wherein R a and R b , and R d and R e are taken together to form oxo or the like； R 4a and R 4b are hydrogen or the like； n is 1 or the like； R 2 is aryl or the like； s and s' is 0 or the like； R 9 and R 9' are halogen or the like； R 20a and R 20b are hydrogen, alkyl or the like； u is 1 to 4； R 13 is hydrogen or the like, or its pharmaceutically acceptable salt.
