Safety arrangement of an elevator, which elevator comprises an elevator control system, an elevator motor, a power supply circuit of the elevator motor as well as at least one mechanical stopping appliance (26, 48) for preventing movement of the elevator car, and which safety arrangement comprises: - a measuring arrangement for monitoring the safety spaces of the elevator - a control unit - a first data transfer channel between the said measuring arrangement and the control unit - a second data transfer channel between the elevator control system and the control unit and which measuring arrangement for monitoring the safety spaces of the elevator comprises: - normal drive limit switches (12, 14) in the upper part and the lower part of the elevator shaft for setting the end limits of movement of the elevator car in normal drive, and wherein the measuring arrangement for monitoring the safety spaces of the elevator comprises: - service space limit switches (13, 15) in the upper part and the lower part of the elevator shaft for setting service spaces in the elevator shaft, which service space limit switches are situated farther from the ends of the elevator shaft than the normal drive limit switches (12, 14), and which measuring arrangement for monitoring the safety spaces of the elevator is characterized by that it comprises: - sensors(7,7',8) that measure the position of the landing door of the elevator, being switches that are connected in series with each other, the contact of which opens when the landing door opens, and - the data transfer channel between the control unit and the switches (7, 7', 8) comprises a resistance (33, 34, 35) fitted in the series circuit in parallel with each aforementioned switch, wherein the resistance fitted in parallel with the switch of the landing door of the bottommost floor differs in its resistance value from the resistances fitted in parallel with all the other switches (7, 7', 8) in order to identify the position of the landing door of the bottommost floor. - a measuring arrangement for monitoring the safety spaces of the elevator - a control unit - a first data transfer channel between the said measuring arrangement and the control unit - a second data transfer channel between the elevator control system and the control unit - normal drive limit switches (12, 14) in the upper part and the lower part of the elevator shaft for setting the end limits of movement of the elevator car in normal drive, and - service space limit switches (13, 15) in the upper part and the lower part of the elevator shaft for setting service spaces in the elevator shaft, which service space limit switches are situated farther from the ends of the elevator shaft than the normal drive limit switches (12, 14), and which measuring arrangement for monitoring the safety spaces of the elevator is characterized by that it comprises: - sensors(7,7',8) that measure the position of the landing door of the elevator, being switches that are connected in series with each other, the contact of which opens when the landing door opens, and - the data transfer channel between the control unit and the switches (7, 7', 8) comprises a resistance (33, 34, 35) fitted in the series circuit in parallel with each aforementioned switch, wherein the resistance fitted in parallel with the switch of the landing door of the bottommost floor differs in its resistance value from the resistances fitted in parallel with all the other switches (7, 7', 8) in order to identify the position of the landing door of the bottommost floor. - sensors(7,7',8) that measure the position of the landing door of the elevator, being switches that are connected in series with each other, the contact of which opens when the landing door opens, and - the data transfer channel between the control unit and the switches (7, 7', 8) comprises a resistance (33, 34, 35) fitted in the series circuit in parallel with each aforementioned switch, wherein the resistance fitted in parallel with the switch of the landing door of the bottommost floor differs in its resistance value from the resistances fitted in parallel with all the other switches (7, 7', 8) in order to identify the position of the landing door of the bottommost floor.