The governing body of each municipal corporation shall, unless otherwise provided by county or city charter, designate one person to serve as budget officer. The budget officer, or the person or department designated by charter and acting as budget officer, shall prepare or supervise the preparation of the budget document. The budget officer shall act under the direction of the executive officer of the municipal corporation, or where no executive officer exists, under the direction of the governing body. [1963 c.576 § 5]