The present invention aims to provide a compound that : has an excellent cytotoxic action on cancer cells, excellent induction of BET protein degradation in cancer cells, and an excellent binding-inhibiting action on BET protein and acetylated histone; and is effective as an anti-cancer agent, a BET protein degradation-inducing agent, or a BET protein inhibiting agent. A compound indicated in general formula (I) or a pharmacologically acceptable salt thereof. {In the formula, each symbol is as outlined in the Description.}