This paper addresses the performance improvement of a multi-action recommendation system that leverages various user behaviors (e.g., purchases, clicks, and cart additions) in e-commerce. Existing systems suffer from a significant performance gap between recommended items visited (items users interact with) and unvisited items. To address this, we propose MEMBER, a novel multi-action recommendation system based on a mixture of experts (MIxture-of-Experts), which utilizes expert models specialized for visited and unvisited items, respectively. Each expert model is trained using self-supervised learning, and experimental results demonstrate up to 65.46% performance improvement (based on a hit ratio of 20) compared to existing systems.