To provide a sleeper of a concrete-made columnar object capable of not only improving productivity but also reducing its weight while holding required strength and facilitating handling such as transportation to improve workability.

This sleeper is constituted in such a way that it is formed like a column by mixing, heating, and melting polyethylene of 59.99 to 80% wts., polypropylene of 19.95 to 40% wts., and foaming agent of 0.01 to 0.05% wts., it forms a predetermined cross sectional shape, it has fixed length, and hollow metallic pipes 2, 12 having predetermined thickness are buried along the direction of length inside it while the pipes 2, 23 remains hollow.