Abstract: An evaporator operating on falling film principle, has a shell (1) with a system (2) of evaporating tubes therein, whereby a liquid to be concentrated is fed on the outer surface of the evaporating tube system (2) and vapor is led to flow inside the tubes of the evaporating tube system (2). The evaporating tube system (2) is formed of evaporating elements, each evaporating element being formed of evaporating tubes (9) substantially on the same level. The upper ends of the tubes are connected to a common collecting chamber (8) and the lower end, respectively, to a common collecting chamber (10) in such a manner that there is a connection between both collecting chambers (8, 10) through each tube (9) between them, due to which the collecting chambers (8) of the upper end of the evaporating elements are interconnected through the upper connecting chamber (12), and respectively, the collecting chambers (10) of the lower end are interconnected through the connecting chamber (13) of the lower end.