A circulation unit is for an arrangement arranged to continuously circulate drilling fluid during drilling. A housing is provided with a center bore which is defined by upper and lower annular sealing elements which are rotatably supported in the housing. The sealing elements are provided with a center opening which, by the expansion of said sealing elements, is closable or fits tightly against a pipe. A gate valve in a closed state forms a fluid-tight partition between upper and lower chambers in the housing. Each of the sealing elements is connected in a fluid-tight manner to a rotatable packer pipe surrounded by a packer assembly that fits tightly against the circumference of the packer pipe and against the housing. An arrangement is for the continuous circulation of drilling fluid during drilling, including as circulation unit arranged between upper and lower rotary units.