A longitudinal profile measuring apparatus including a relative distance meter located on a frame supported by more than two wheels in a row in a direction of a measuring line for measuring relative distance to a target surface, a moving distance meter for measuring moving distance of movement along the measuring line on the target surface, and a data processing unit for finding spatial data, which shows a rough profile of the target surface, along the measuring line from the relative distance measured by the relative distance meter. The data processing unit storing moving distance data associated with relative distance data to the target surface and transforming the relative distance data of the stored data into amplitude corresponding to frequency, multiplying the amplitude corresponding to frequency by a coefficient of correction for allowing the apparatus to have a gain with a desired frequency characteristic for correction, and inverse transforming the corrected amplitude to find the corrected spatial data of the target surface.