The present invention relates to a phenacylamine derivative of the formula (I) or a salt thereof: ##STR00001## wherein A is alkyl, cycloalkyl, phenyl which may be substituted by Y, pyridyl which may be substituted by Y, or pyrazolyl which may be substituted by Y, R.sub.1 and R.sub.2 are each alkyl, or R.sub.1 and R.sub.2 may together form a 3- to 6-membered saturated carbocycle, R.sub.3 is hydrogen, alkyl, alkoxyalkyl, alkylthioalkyl or COR.sub.4, X is halogen, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkoxy, haloalkoxy, alkenyloxy, haloalkenyloxy, alkynyloxy, haloalkynyloxy, alkylthio, haloalkylthio, alkenylthio, haloalkenylthio, alkynylthio, haloalkynylthio, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, dialkylaminosulfonyl, nitro, cyano, phenyl which may be substituted by Y, phenoxy which may be substituted by Y, benzyloxy which may be substituted by Y, or pyridyloxy which may be substituted by Y, and n is an integer of from 0 to 5.