The present invention provides a bioreactor having a system that can grow cells, tissue, etc. while maintaining or improving their function, and finally recover the cells as they are with good efficiency. The bioreactor has a porous sheet-form material disposed in its main body, the porous sheet-form material being formed from a nonwoven fabric, etc. having high cell affinity in order to retain cells. This porous sheet-form material has a thermosensitive polymer and a cell-adhesive substance incorporated thereinto, and the porous sheet-form material is not only cell-adhesive but also allows cells and tissue to be detached from the porous sheet-form material as they are by, for example, cooling from 37° C. to 25° C. Furthermore, in order to efficiently ensure the bioactivity or the survival of the cells, it is arranged so that circulation of a culture medium in a culturing space of the bioreactor is of a radial flow type.