The present invention provides a quinolone compound that inhibits the chronic progression of Parkinson's disease or protects dopamine neurons from disease etiology, thereby suppressing the progression of neurological dysfunction, so as to prolong the period of time until L-dopa is administered while also improving neuronal function; the quinolone compound of the invention is represented by Formula (1): wherein: R1 represents hydrogen or the like; R2 represents hydrogen or the like; R3 represents substituted or unsubstituted phenyl or the like; R4 represents halogen or the like; R5 represents hydrogen or the like; R6 represents hydrogen or the like; and R7 represents hydrogen or the like.