A photobioreactor with a microalgae's cultivation chamber in the form of a duct that is constructed from an inflatable sleeve from transparent polymer film; this inflatable sleeve excluding its terminal sections is sandwiched between a bank of frames with wire nettings from below and glass panes from above the inflatable sleeve, and it has a small inclination regarding the horizontal plane. The terminal sections of the inflatable sleeve are in fluid communication with two headers, which are used for supplying and removal of gaseous medium and suspension of microalgae into and out of the duct.