How do you make a bank account without a job?

Hi everyone. I've found a job contract but I can't finish signing it until I have a Japanese bank account. I've tried opening one with Japan Post (ゆうちょ銀行) but they told me that I need to have a job already. How the hell does that work? Isn't that a catch 22? I told them about my contract but it didn't do much for them.