To provide a cellulose/polyolefin-based composite material excelling in both balance of physical properties and a linear expansion characteristic, and easily manufacturable.

This cellulose/polyolefin-based composite material contains (A) cellulose nonwoven fabric, (B) modified polyolefin having a functional group, and (C) polyolefin. This method is used for manufacturing the cellulose/polyolefin-based composite material by immersing or applying (B) the modified polyolefin having a functional group in/to (A) the cellulose nonwoven fabric, and thereafter sticking (C) the polyolefin thereto.