The present invention relates to a dendrite elongation inhibitor for melanocytes consisting of a compound represented by the following general formula (1): ##STR00001## and/or a salt thereof, wherein R.sub.1, R.sub.2, and R.sub.3 each independently represent a C.sub.1-4 alkyl group or hydrogen atom, and a skin preparation for external use comprising the dendrite elongation inhibitor for melanocytes as an active ingredient.