English version comes after Japanese.
月末をもって退職する場合は、退職日が本当に月末の日にちになっているか注意が必要です。1日前にされると翌日に社会保険の資格を喪失してしまい、切れ目なく転職したつもりが１ヶ月空白が出来てしまいます。
It's very common in Japan that employees take the remaining annual leaves right before the official last day at work. For example, if you left your employer on the 31st of July, you'd take the remaining 30 days annual leaves so your actual last day could be the 18th of June. Yes, I'm serious. It happens.