A polyphenylene ether resin composition includes a modified polyphenylene ether copolymer, a high-molecular-weight compound, and a crosslinking agent for the modified polyphenylene ether copolymer. The modified polyphenylene ether copolymer includes a substituent having a carbon-carbon unsaturated double bond at a molecular chain end of the modified polyphenylene ether copolymer. The high-molecular-weight compound has a glass transition temperature (Tg) measured by differential scanning calorimetry of 20° C. or lower and has a number-average molecular weight Mn ranging from 1000 to 10000, inclusive. The crosslinking agent includes at least two carbon-carbon unsaturated double bonds per molecule, and includes at least one of dicyclopentadiene acrylate and dicyclopentadiene methacrylate. In a cured state of the polyphenylene ether resin composition, the modified polyphenylene ether copolymer is phase separated from the high-molecular-weight compound.