It is provided a fluid-treatment device (1) comprising a base (2) adapted to be coupled in a fluid-tight manner to a casing (5) defining a chamber (5a) suitable to receive a fluid and made up of at least one plate (3) provided with at least one through hole (4) adapted to enable passage of the fluid through the plate itself; at least one circulation element (7) defining part of a duct (6) in communication for fluid passage with the through hole (4); and said plate (3) having, in the vicinity of at least one of the through holes (4), a connecting profile (8) of one piece construction with the plate (3), which is made integral with the circulation element (7) through end-to-end welding and defines a portion of one said duct (6).
