A pyrimidone derivative represented by formula (I) or a salt thereof, or a solvate thereof or a hydrate thereof: wherein : X represents a methylene, NH, a nitrogen atom substituted by a C(O)-O-(C 1-6 -alkyl) group； R1 represents a 2, 3 or 4-pyridine ring or a 2, 4 or 5-pyrimidine ring, the ring being optionally substituted by a C 1-6 alkyl group, a C 1-6 alkoxy group or a halogen atom； R2 represents a hydrogen atom, a C 1-6 alkyl group or a halogen atom； R3 represents a C 1-6 alkyl group optionally substituted, R4 represents a hydrogen atom, a halogen atom, a hydroxyl group, a C 1-6 alkyl group； m represents 1 to 2 when X is a methylene or m represents2 when X is NH, a nitrogen atom substituted by a C(O)-O-(C 1-6 -alkyl) group ； in the form of a free base or of an addition salt with an acid. Use in therapeutic
