Protein-binding drug

Provided is a compound that, after administration into an organism, rapidly binds to blood albumin, persistently circulates systemically, and efficiently accumulates in tumor tissue and then releases an active drug. The compound exhibits a high concentration in tumor tissue, an excellent anti-tumor effect, and reduced adverse effects. The present invention provides a compound represented by general formula (I) [the definitions of the individual symbols in the formula are as described in the Description] or a pharmaceutically acceptable salt thereof, which can provide an excellent anti-cancer agent that exhibits an excellent anti-cancer action on cancer cells while producing few adverse effects.