An automatic door sensor device that is supported by a support member and detects an object to control opening and closing of a door, the device comprising: a doorway area sensor to detect presence of an object in a doorway area which includes at least a portion of an area defined by the path of the door; and a detector (6,7b) to detect presence and/or movement of an object in a changeable detection area (A,C2,C3); and a detection area changer to change the detection area (A, C2, C3), when it is determined that the door is transitioning from an open position to a closed position, so as to avoid erroneously detecting the transitioning door, characterized by a processing circuit which comprises: a condition determiner to determine a predetermined condition in which the detector (6,7b) detects neither presence nor movement of an object in the detection area (A,C2,C3) and the doorway area sensor detects no presence of an object in the doorway area, and a doorway area determiner to determine whether, when the predetermined condition is determined by the condition determiner, the doorway area sensor detects presence of an object in the doorway area immediately after the predetermined condition, and to determine that the door is transitioning from an open position to a closed position based on the fact that the doorway area determiner determines the presence of an object in the doorway area immediately after the predetermined condition. a doorway area sensor to detect presence of an object in a doorway area which includes at least a portion of an area defined by the path of the door; and a detector (6,7b) to detect presence and/or movement of an object in a changeable detection area (A,C2,C3); and a detection area changer to change the detection area (A, C2, C3), when it is determined that the door is transitioning from an open position to a closed position, so as to avoid erroneously detecting the transitioning door, characterized by a processing circuit which comprises: a condition determiner to determine a predetermined condition in which the detector (6,7b) detects neither presence nor movement of an object in the detection area (A,C2,C3) and the doorway area sensor detects no presence of an object in the doorway area, and a doorway area determiner to determine whether, when the predetermined condition is determined by the condition determiner, the doorway area sensor detects presence of an object in the doorway area immediately after the predetermined condition, and to determine that the door is transitioning from an open position to a closed position based on the fact that the doorway area determiner determines the presence of an object in the doorway area immediately after the predetermined condition. a condition determiner to determine a predetermined condition in which the detector (6,7b) detects neither presence nor movement of an object in the detection area (A,C2,C3) and the doorway area sensor detects no presence of an object in the doorway area, and a doorway area determiner to determine whether, when the predetermined condition is determined by the condition determiner, the doorway area sensor detects presence of an object in the doorway area immediately after the predetermined condition, and to determine that the door is transitioning from an open position to a closed position based on the fact that the doorway area determiner determines the presence of an object in the doorway area immediately after the predetermined condition.