Wavefront sensing from an extended object is a challenging task since the phase to be sensed is disturbed by the one generated from the structure of the extended object. To address this problem, a general wavefront sensor is proposed. The configuration of the proposed sensor consists of a field lens, a collimating lens, a lenslet array, and a camera. The field lens, the first element of this sensor, ensures that each lenslet collects the same information of the extended object, which is a basis for the reconstruction of the distorted wavefront from the extended object using the proposed sensor. The fundamental strategy of the sensor is converting the scenario of wavefront sensing from an extended object into the traditional one from a point source by eliminating the Fourier spatial spectrum of the extended object in the frequency domain. As a result, the distorted wavefront can be reconstructed using the algorithm of the Shack–Hartmann wavefront sensor. Numerical simulations and experiments both verify the feasibility and accuracy of the proposed sensor for direct wavefront sensing from any types of extended objects.