To provide a polypropylene sheet reducing a "drawdown" phenomenon occurring when the polypropylene sheet is used to be subjected to vacuum forming and excellent in moldability.

Additives are mixed with a raw material resin comprising 50-100 pts.wt. of a polypropylene powder and 0-50 pts.wt. of polypropylene pellets to be kneaded with the raw material resin in an extruder and the kneaded mixture is directly cooled through a T-die to be taken up to manufacture the polypropylene sheet. In the manufacturing method, the processes, which are performed up to the time just before the polypropylene powder is supplied to the extruder for the purpose of kneading, are kept under an inert gas atmosphere.