A release device for releasably connecting a downhole object, such as a running tool or a plug, to a setting tool, the release device extending between a proximal end adapted to be coupled to the setting tool and a distal end adapted to be coupled to the downhole object, the release device comprising: - a base element extending in a longitudinal direction, characterised in that the release device further comprises: - a connecting element arranged in continuation of the base element, the connecting element constituting the distal end of the release device and being adapted to be coupled to the downhole object, wherein the connecting element is releasably coupled to the base element by an activatable release mechanism comprising an activatable locking sleeve slidable in the longitudinal direction and a key element having a plurality of key fingers flexible in an inwards radial direction and adapted to latch onto the connecting element, the inwards flexibility of the key fingers being controlled by the position of the locking sleeve, and wherein the release mechanism further comprises a release spring forcing the locking sleeve and the key element in mutually opposite directions, and where the activatable locking sleeve is hydraulically activated by injection of a hydraulic fluid into an expandable space, defined, at least partly, by a piston face of the locking sleeve, whereby hydraulic fluid supplied under pressure to the expandable space forces the locking sleeve in a direction towards the distal end of the release device, thereby compressing the release spring, and wherein activation of the locking sleeve, causes the release spring to force the locking sleeve into a release position, thereby activating the release mechanism and allowing separation of the connecting element from the base element. - a base element extending in a longitudinal direction, characterised in that the release device further comprises: - a connecting element arranged in continuation of the base element, the connecting element constituting the distal end of the release device and being adapted to be coupled to the downhole object, wherein the connecting element is releasably coupled to the base element by an activatable release mechanism comprising an activatable locking sleeve slidable in the longitudinal direction and a key element having a plurality of key fingers flexible in an inwards radial direction and adapted to latch onto the connecting element, the inwards flexibility of the key fingers being controlled by the position of the locking sleeve, and wherein the release mechanism further comprises a release spring forcing the locking sleeve and the key element in mutually opposite directions, and where the activatable locking sleeve is hydraulically activated by injection of a hydraulic fluid into an expandable space, defined, at least partly, by a piston face of the locking sleeve, whereby hydraulic fluid supplied under pressure to the expandable space forces the locking sleeve in a direction towards the distal end of the release device, thereby compressing the release spring, and wherein activation of the locking sleeve, causes the release spring to force the locking sleeve into a release position, thereby activating the release mechanism and allowing separation of the connecting element from the base element.