A stilbene derivative of the following general formula (I) or a pharmaceutically acceptable acid addition salt thereof have low toxicity, but are water soluble and effective as carcinostatics: ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3, which may be the same or different, each represent an alkyl group having 1 to 3 carbon atoms; X represents a hydrogen atom or a nitrile group; Y represents an alkyloxy group having 1 to 3 carbon atoms, an alkyl group having 1 to 6 carbon atoms or a halogen atom.