A method of producing a polypropylene resin in-mold expanded product, includes: placing polypropylene resin particles obtained from a base material resin having a melting point of 140° C. to 150° C., the base material resin comprising: a polypropylene resin A comprising 3 weight % to 15 weight % of 1-butene and having a melting point of 130° C. to 140° C.; and a polypropylene resin B having a melting point of 145° C. to 165° C., water, and an inorganic gas foaming agent in a pressure-resistant container, forming a mixture, dispersing the polypropylene resin particles while stirring the mixture, obtaining a dispersion liquid, increasing a temperature and a pressure in the pressure-resistant container, releasing the dispersion liquid from the pressure-resistant container into a region having a pressure lower than the pressure in the pressure-resistant container, producing expanded polypropylene resin particles; and filling a mold with the expanded polypropylene resin particles, and then heating the expanded polypropylene resin particles.