Theoretical methods in planning the wake adapted propeller and the cavitation free propeller are being suggested in foreign lands nowadays. Almost all of these methods are to design the optimum propeller by the lifting-line theory and to amend the camber ratio and pitch ratio by the theory of wide-bladed propeller advocated by Ludwieg & Ginzel and Lerbs. The theory of the wide-bladed propellers has been published also by Strscheletzky, Yamasaki and others, in addition to the above stated three. However, there are defects in those theories, theoretical and practical, and the counting methods are very much complicated. The author has developed a new theory of the wide-bladed propellers by applying De Young's theory of the low aspect ratio wings of arbitrary plan forms to propellers.