A compound represented by the following general formula (1) or a salt thereof. R1 represents a halogen atom and so on; R2 and R3 each represent a hydrogen atom and so on; R4 and R5 each represent a hydrogen atom and so on, or R4 and R5 may form an oxo group; Ra and Rb each represent a lower alkyl group optionally having a substituent and so on, or they may bind to each other to form a nitrogen-containing heterocyclic ring which may be substituted by one or plural Rc; Rc represents an aryl group optionally having a substituent and so on; ring A represents a benzene ring and so on; and m represents 0, 1 or 2.