A treatment apparatus, in particular filter apparatus, for a fluid, in particular for a liquid fluid, having a replaceable treatment unit featuring a housing having a housing pot, a housing cover, at least one inlet for the fluid to be treated and at least one outlet for the treated fluid, and having a connecting head featuring at least one supply line for the fluid to be treated which is connectable to the at least one inlet, and/or at least one discharge line for the treated fluid which is connectable to the at least one outlet, wherein the connecting head and the treatment unit are connectable to each other using a releasable bayonet-type connecting means by executing a plug-in/rotational motion around a connecting axis of the treatment apparatus, and the connecting means features at least one housing connecting part on the side of the housing and at least one head connecting part on the side of the connecting head, which are actively connectable to one another to be able to make a connection of the connecting means, wherein the housing connecting part and the head connecting part respectively feature at least one functional element (44, 104) complementary to each other in the circumferential direction around the connecting axis and which are actively connectable to one another, characterized in that the at least one of the functional elements (44, 104) complementary to each other features a mounting ramp (43, 103) which leads, with regard to the connecting axis, into a perpendicular support area (45, 105) and the other one of the functional elements (104, 44) complementary to each other features a sliding area (142, 42) which is, with regard to the connecting axis, adjoined by a perpendicular support area (105, 45), wherein in a connecting end position of the connecting means the two support areas (45, 105) are positioned one above the other with respect to the connecting axis, wherein one or a plurality of support areas (45, 105) of at least one functional element (44, 104) are provided whose total length in the circumferential direction is at least 20% of a corresponding circumference on the same radius of the housing connecting part and/or of a corresponding circumference on the same radius of the head connecting part. wherein the connecting head and the treatment unit are connectable to each other using a releasable bayonet-type connecting means by executing a plug-in/rotational motion around a connecting axis of the treatment apparatus, and the connecting means features at least one housing connecting part on the side of the housing and at least one head connecting part on the side of the connecting head, which are actively connectable to one another to be able to make a connection of the connecting means, wherein the housing connecting part and the head connecting part respectively feature at least one functional element (44, 104) complementary to each other in the circumferential direction around the connecting axis and which are actively connectable to one another, characterized in that the at least one of the functional elements (44, 104) complementary to each other features a mounting ramp (43, 103) which leads, with regard to the connecting axis, into a perpendicular support area (45, 105) and the other one of the functional elements (104, 44) complementary to each other features a sliding area (142, 42) which is, with regard to the connecting axis, adjoined by a perpendicular support area (105, 45), wherein in a connecting end position of the connecting means the two support areas (45, 105) are positioned one above the other with respect to the connecting axis, wherein one or a plurality of support areas (45, 105) of at least one functional element (44, 104) are provided whose total length in the circumferential direction is at least 20% of a corresponding circumference on the same radius of the housing connecting part and/or of a corresponding circumference on the same radius of the head connecting part.