A surface shape measuring device (10, 100) configured to measure a surface shape of a workpiece by detecting a displacement of a probe (28, 128) being in contact with a surface of the workpiece with a detector (26, 126) while rotating the workpiece relatively to the detector (26, 126) around a rotational center, the device comprising: a first shape data acquiring unit (38, 138) configured to acquire first shape data with the detector (26, 126) being disposed on one side with respect to the workpiece, the first shape data indicating the surface shape of the workpiece when detecting a displacement of the surface of the workpiece with the detector (26, 126) while rotating the workpiece relatively to the detector (26, 126) around the rotational center; a second shape data acquiring unit (40, 140) configured to acquire second shape data with the detector (26, 126) being disposed on the other side with respect to the workpiece, the second shape data indicating the surface shape of the workpiece when detecting a displacement of the surface of the workpiece with the detector (26, 126) while rotating the workpiece relatively to the detector (26, 126) around the rotational center; a shape parameter calculating unit configured to collate the first shape data and the second shape data with each other, and calculate a shape parameter defining the surface shape of the workpiece based on a result of the collation;. a misalignment amount calculating unit configured to collate the first shape data and the second shape data with each other, and calculate a misalignment amount indicating a distance from the detection point to a measurement generating line based on a result of the collation, where the measurement generating line indicates a straight line that passes through the rotational center and is parallel to a displacement direction of the probe (28, 128), and the detection point indicates a position at which the probe (28, 128) comes into contact with the workpiece. a first shape data acquiring unit (38, 138) configured to acquire first shape data with the detector (26, 126) being disposed on one side with respect to the workpiece, the first shape data indicating the surface shape of the workpiece when detecting a displacement of the surface of the workpiece with the detector (26, 126) while rotating the workpiece relatively to the detector (26, 126) around the rotational center; a second shape data acquiring unit (40, 140) configured to acquire second shape data with the detector (26, 126) being disposed on the other side with respect to the workpiece, the second shape data indicating the surface shape of the workpiece when detecting a displacement of the surface of the workpiece with the detector (26, 126) while rotating the workpiece relatively to the detector (26, 126) around the rotational center; a shape parameter calculating unit configured to collate the first shape data and the second shape data with each other, and calculate a shape parameter defining the surface shape of the workpiece based on a result of the collation;. a misalignment amount calculating unit configured to collate the first shape data and the second shape data with each other, and calculate a misalignment amount indicating a distance from the detection point to a measurement generating line based on a result of the collation, where the measurement generating line indicates a straight line that passes through the rotational center and is parallel to a displacement direction of the probe (28, 128), and the detection point indicates a position at which the probe (28, 128) comes into contact with the workpiece.