The present invention provides a transdermal preparation excellent in transdermal absorbability using various active ingredients by virtue of a transdermal absorption enhancement aid or a transdermal absorption enhancer comprising an equimolar salt of a) a basic functional group-containing compound having a molecular weight of from 50 to 120 and a melting point of from 50 to 350°C, and b) an acidic functional group-containing compound having a LogP of -4 to 7.3.
