Apparatus for aligning guide rails and landing doors in an elevator shaft being provided with at least car guide rails (51, 52) at opposite side walls (21C, 21D) of the elevator shaft, a first direction extending upwards and downwards in the vertically extending elevator shaft, a second direction extending between the car guide rails (51, 52) and a third direction being perpendicular to the second direction, the second direction and the third direction extending in a coinciding plane or in parallel planes, characterized in that the apparatus comprises: a frame, a first pair of actuators (210, 220) being positioned on a first side of the frame, each actuator (210, 220) comprising a support arm (212, 222) being movable in the second direction, each actuator (210, 220) being supported on the frame with a support mechanism (310, 320) being movable in the third direction, whereby outer ends of the support arms (212, 222) abut a first side wall of the elevator shaft when moved outwardly in relation to the frame, a second pair of actuators (230, 240) being positioned on a second opposite side of the frame, each actuator (230, 240) comprising a support arm (232, 242) being movable in the second direction, each actuator (230, 240) being supported on the frame with a support mechanism (330, 340) being movable in the third direction, whereby outer ends of the support arms (232, 242) abut a second opposite side wall of the elevator shaft when moved outwardly in relation to the frame, first gripping means (411, 412) being supported on the first side of the frame and second gripping means (421, 422) being supported on the second opposite side of the frame, the first gripping means (411, 412) being adapted to grip a first car guide rail and the second gripping means (421, 422) being adapted to grip a second opposite car guide rail, measuring means (510, 520) being attached to opposite sides of the frame in the vicinity of the first gripping means (411, 412) and the second gripping means (421, 422), said measuring means (510, 520) being used to determine the position of the apparatus in the elevator shaft, whereby the frame can be positioned in a desired horizontal position in relation to the elevator shaft with the opposite pairs of support arms (212, 222, 232, 242) moving in the second direction and the respective support mechanisms (310, 320, 330, 340) moving in the third direction and the opposite car guide rails (51, 52) being locked in the gripping means (411, 412) can be adjusted in relation to each other and in relation to the elevator shaft with the apparatus. a frame, a first pair of actuators (210, 220) being positioned on a first side of the frame, each actuator (210, 220) comprising a support arm (212, 222) being movable in the second direction, each actuator (210, 220) being supported on the frame with a support mechanism (310, 320) being movable in the third direction, whereby outer ends of the support arms (212, 222) abut a first side wall of the elevator shaft when moved outwardly in relation to the frame, a second pair of actuators (230, 240) being positioned on a second opposite side of the frame, each actuator (230, 240) comprising a support arm (232, 242) being movable in the second direction, each actuator (230, 240) being supported on the frame with a support mechanism (330, 340) being movable in the third direction, whereby outer ends of the support arms (232, 242) abut a second opposite side wall of the elevator shaft when moved outwardly in relation to the frame, first gripping means (411, 412) being supported on the first side of the frame and second gripping means (421, 422) being supported on the second opposite side of the frame, the first gripping means (411, 412) being adapted to grip a first car guide rail and the second gripping means (421, 422) being adapted to grip a second opposite car guide rail, measuring means (510, 520) being attached to opposite sides of the frame in the vicinity of the first gripping means (411, 412) and the second gripping means (421, 422), said measuring means (510, 520) being used to determine the position of the apparatus in the elevator shaft, whereby the frame can be positioned in a desired horizontal position in relation to the elevator shaft with the opposite pairs of support arms (212, 222, 232, 242) moving in the second direction and the respective support mechanisms (310, 320, 330, 340) moving in the third direction and the opposite car guide rails (51, 52) being locked in the gripping means (411, 412) can be adjusted in relation to each other and in relation to the elevator shaft with the apparatus.