A map data generator comprising: - a measurement-data acquiring unit configured to acquire, as a measurement data piece, a plurality of image data pieces in two dimensions and a distance data piece, the plurality of image data pieces being continuously imaged, and each having an imaging range partly overlapping an imaging range of at least one of the other image data pieces, the distance data piece indicating a distance to an object within each of the plurality of image data pieces; - a measurement data database configured to relate the acquired measurement data piece with a time data piece to store the acquired measurement data piece and the time data piece, the time data piece being used for linking the measurement data piece in chronological order to store the measurement data piece in a database; - a map-data generating unit configured to update a map data piece in three dimensions generated based on a plurality of the measurement data pieces, every time the measurement data piece is acquired; - a map data database configured to relate the map data piece that is sequentially updated with the time data piece corresponding to the measurement data piece used when the map data piece is updated, to store the map data piece and the time data piece; - an input unit configured to receive an input of a designated time as desired; and characterized by an edit unit configured to check, as the time data piece, the designated time, received in the input unit, against the map data database to identify the map data piece corresponding to the designated time, - wherein upon the receipt of the designated time in the input unit, the map-data generating unit redoes the update of the map data piece identified by the edit unit, using the measurement data piece newly acquired after the designated time is received in the input unit. - a measurement-data acquiring unit configured to acquire, as a measurement data piece, a plurality of image data pieces in two dimensions and a distance data piece, the plurality of image data pieces being continuously imaged, and each having an imaging range partly overlapping an imaging range of at least one of the other image data pieces, the distance data piece indicating a distance to an object within each of the plurality of image data pieces; - a measurement data database configured to relate the acquired measurement data piece with a time data piece to store the acquired measurement data piece and the time data piece, the time data piece being used for linking the measurement data piece in chronological order to store the measurement data piece in a database; - a map-data generating unit configured to update a map data piece in three dimensions generated based on a plurality of the measurement data pieces, every time the measurement data piece is acquired; - a map data database configured to relate the map data piece that is sequentially updated with the time data piece corresponding to the measurement data piece used when the map data piece is updated, to store the map data piece and the time data piece; - an input unit configured to receive an input of a designated time as desired; and characterized by an edit unit configured to check, as the time data piece, the designated time, received in the input unit, against the map data database to identify the map data piece corresponding to the designated time, - wherein upon the receipt of the designated time in the input unit, the map-data generating unit redoes the update of the map data piece identified by the edit unit, using the measurement data piece newly acquired after the designated time is received in the input unit.