Locking device for a flap or a door, comprising a substantially flat support structure , a handle element for unlocking the locking device; and a latch with a hook ; wherein: the support structure can be non-positively connected to the flap and has - a pivot bearing for a rotation bolt ; and - at least one cylindrical straight-guiding plain bearing bush ; the handle element has - a handle recess and at least one plain bearing bolt and - provides a receptacle for an activation bolt arranged in a fixed position in the handle element and aligned at right angles to the plain bearing bolt; the latch has - a slotted link designed as an elongated hole or groove for guiding the activation bolt ; wherein, in a pre-assembled state, - the plain bearing bolt of the handle element is guided in a longitudinally displaceable manner in the plain bearing bush of the support structure ; - the latch is rotatably mounted in the pivot bearing of the support structure about the rotation bolt between a "locked" and "open" position; and - the activation bolt is in engagement with the slotted link , characterized in that the guidance of the handle element is carried out in a straight line during opening and closing by the combination of plain bearing bolt /plain bearing bush and this straight-line movement is translated by the co-moved activation bolt via the slotted link into a rotary movement of the latch , which causes the unlocking of the locking device. the support structure can be non-positively connected to the flap and has - a pivot bearing for a rotation bolt ; and - at least one cylindrical straight-guiding plain bearing bush ; - a pivot bearing for a rotation bolt ; and - at least one cylindrical straight-guiding plain bearing bush ; the handle element has - a handle recess and at least one plain bearing bolt and - provides a receptacle for an activation bolt arranged in a fixed position in the handle element and aligned at right angles to the plain bearing bolt; - a handle recess and at least one plain bearing bolt and - provides a receptacle for an activation bolt arranged in a fixed position in the handle element and aligned at right angles to the plain bearing bolt; the latch has - a slotted link designed as an elongated hole or groove for guiding the activation bolt ; - a slotted link designed as an elongated hole or groove for guiding the activation bolt ; wherein, in a pre-assembled state, - the plain bearing bolt of the handle element is guided in a longitudinally displaceable manner in the plain bearing bush of the support structure ; - the latch is rotatably mounted in the pivot bearing of the support structure about the rotation bolt between a "locked" and "open" position; and - the activation bolt is in engagement with the slotted link , - the plain bearing bolt of the handle element is guided in a longitudinally displaceable manner in the plain bearing bush of the support structure ; - the latch is rotatably mounted in the pivot bearing of the support structure about the rotation bolt between a "locked" and "open" position; and - the activation bolt is in engagement with the slotted link , characterized in that the guidance of the handle element is carried out in a straight line during opening and closing by the combination of plain bearing bolt /plain bearing bush and this straight-line movement is translated by the co-moved activation bolt via the slotted link into a rotary movement of the latch , which causes the unlocking of the locking device. <EOS>