The present invention provides 2-aminoquinazoline derivatives represented by formula (I): wherein R1 and R2 may be the same or different and each represents a hydrogen atom, substituted or unsubstituted lower alkyl, and the like; X represents a bond or CR7aR7b wherein R7a and R7b may be the same or different and each represents a hydrogen atom, and the like; when X is a bond, R3 represents substituted or unsubstituted aryl or a substituted or unsubstituted aromatic heterocyclic group; when X is CR7aR7b wherein R7a and R7b have the same meanings as defined above, respectively, R3 represents substituted or unsubstituted lower alkoxy, substituted or unsubstituted aryl, and the like; R4 represents a hydrogen atom, hydroxy, substituted or unsubstituted lower alkoxy, and the like; and R5 represents a hydrogen atom, substituted or unsubstituted aryl, and the like, or a pharmaceutically acceptable salt thereof.