<p>Disclosed is a pharmaceutical agent which can inhibit the chronic progression of Parkinson's disease or protect dopamine neurons from a causal factor of the disease to inhibit the progression of nervous system dysfunction, thereby extending the period up to the administration of L-DOPA, and which has a function-improving effect. Specifically disclosed is a pharmaceutical agent comprising a quinolone compound represented by general formula (1) [wherein R1 represents a hydrogen atom or the like; R2 represents a hydrogen atom or the like; R3 represents a phenyl group which may have a substituent, or the like; R4 represents a hydrogen atom or the like; R5 represents a hydrogen atom or the like; R6 represents a hydrogen atom or the like; and R7 represents a hydroxy group or the like] or a salt thereof.</p>