The invention is a polyrotaxane monomer (A) having a composite molecular structure composed of cyclic molecules and an axial molecule that skewer-like threads through the rings of the cyclic molecules and has a bulky group at both ends thereof so as not to dethread the rings, and the polyrotaxane monomer has a polymerizable functional group in the molecule and has a water content of 5000 ppm or less. According to the present invention, there can be provided a polyrotaxane monomer having a high productivity and capable of producing a high-quality material at a high yield, while maintaining excellent mechanical characteristics of the polyrotaxane monomer.