Surface shape measuring device and surface shape measurement method

A surface shape measuring device that acquires an observation image of a measurement target while causing an optical head to scan relatively to the measurement target in a direction perpendicular to the measurement target, the surface shape measuring device comprising:

• a camera configured to capture the observation image acquired by the optical head;
• a drive unit configured to cause the optical head to scan relatively to the measurement target in a scanning direction perpendicular to the measurement target;
• an encoder configured to detect a position of the optical head in the scanning direction with respect to the measurement target;
• an imaging instructing unit configured to instruct the camera to capture the observation image based on a position signal output from the encoder for each predetermined interval;
• a frame dropping occurrence rate calculating unit configured to calculate a frame dropping occurrence rate indicating an occurrence rate of frame dropping of the camera;
• and
• a measurement condition setting unit configured to set a measurement condition for measuring a surface shape of the measurement target based on the frame dropping occurrence rate.