A road surface shape measuring device that measures a shape of a road surface having undulation, the road surface shape measuring device comprising: a road surface information acquisition unit that acquires pieces of road surface information (I, I-1 to I-n) for a plurality of points on the road surface, the road surface information (I, I-1 to I-n) including a road surface position of the road surface on a reference plane divided into a plurality of segmented regions (G1 to G87), and a road surface height indicating a height from the reference plane of the road surface at the road surface position; a road surface shape determining unit that determines a shape of a part or all of the road surface by estimating a surface shape using the road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) for each segmented region (G1 to G87), when the number of pieces of road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) in which the surface shape is to be estimated increases as compared with the number at the time of previous estimation of the surface shape, the road surface shape determining unit updates the previously estimated surface shape using the road surface information (I, I-1 to I-n) of which the number of pieces has increased, the road surface shape measuring device being characterized in that the road surface shape determining unit estimates a surface shape function that is calculated by fitting a predetermined function to the road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) as the surface shape in the segmented region (G1 to G87), the predetermined function includes a first shape function representing a step on the road surface and a second shape function representing an inclined plane on the road surface, and the road surface shape determining unit estimates the surface shape function further matching the road surface information (I, 1-1 to I-n) included in the segmented region (G1 to G87) among the first shape function and the second shape function as the surface shape function. a road surface information acquisition unit that acquires pieces of road surface information (I, I-1 to I-n) for a plurality of points on the road surface, the road surface information (I, I-1 to I-n) including a road surface position of the road surface on a reference plane divided into a plurality of segmented regions (G1 to G87), and a road surface height indicating a height from the reference plane of the road surface at the road surface position; a road surface shape determining unit that determines a shape of a part or all of the road surface by estimating a surface shape using the road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) for each segmented region (G1 to G87), when the number of pieces of road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) in which the surface shape is to be estimated increases as compared with the number at the time of previous estimation of the surface shape, the road surface shape determining unit updates the previously estimated surface shape using the road surface information (I, I-1 to I-n) of which the number of pieces has increased, the road surface shape measuring device being characterized in that the road surface shape determining unit estimates a surface shape function that is calculated by fitting a predetermined function to the road surface information (I, I-1 to I-n) included in the segmented region (G1 to G87) as the surface shape in the segmented region (G1 to G87), the predetermined function includes a first shape function representing a step on the road surface and a second shape function representing an inclined plane on the road surface, and the road surface shape determining unit estimates the surface shape function further matching the road surface information (I, 1-1 to I-n) included in the segmented region (G1 to G87) among the first shape function and the second shape function as the surface shape function.