A shape measuring apparatus of the present invention measures a variation in a thickness of an object to be measured WA based on an A surface reference interference light and an A surface measuring interference light obtained by performing optical heterodyne interference on a first A surface measuring light and a second A surface measuring light and a B surface reference interference light and a B surface measuring interference light obtained by performing the optical heterodyne interference on a first B surface measuring light and a second B surface measuring light. When the optical heterodyne interference is performed, the shape measuring apparatus makes the first A surface measuring light and the second B surface measuring light equal in frequency and makes the first B surface measuring light and the second A surface measuring light equal in frequency.