The present invention relates to a novel bioreactor system for cell cultivation. More specifically, the invention relates to a compact bioreactor system which has several integrated functions and enables small scale static culture as well as scale-up rocking culture in the same bioreactor. The bioreactor system comprises tray for positioning of a cell culture bag having adjustable volume, a lid covering the cell culture bag and provided with heating function, an integrated perfusion unit, an integrated cell loading unit, and an integrated unit for automatic cell culture sampling, wherein the bioreactor system is controlled by a single control unit. The invention also relates to a method of cell culture using the bioreactor system for culture of therapeutic cells.