Recently, the position sensitive proportional counter (PSPC) has been becoming popular as a detector for X-ray stress measurement. However, little information is available in the literature regarding the effects of specimen mis-setting and/or collimator misalignment on the stress measurement. This is because many factors such as the stress and the X-ray diffraction broadening of specimen, the X-ray focus size, the dimensions of the collimator, the PSPC and the goniometer, et al., are complicatedly related to the effects of specimen mis-setting and/or collimator mis-alignment. The authors have presented a model of Ω assembly X-ray stress measurement using a PSPC as the detector enabling us to simulate the stress measurement under the various conditions including specimen mis-setting and/or collimator misalignment. And they have successfully reported on their effects to the stress measurement.In this paper, the incident beam methods with and without focusing are discussed using the model and the simulation method of the Ω assembly X-ray stress measurement from the view of the collimator intrinsic stress and the stress errors caused by specimen mis-setting and collimator/slit misalignment. The incident beams treated are point focus beam, collimated beam and parallel beam. As the conclusions obtained by this study, it was found that the parallel beam method gives smaller intrinsic stress than the other incident beams do. It was also found that it is possible to reduce the intrinsic stress using the focusing method for the point focused beam and collimated beam. It was demonstrated that the focusing method with the point focused beam and/or collimated beam makes the stress measurement sensitive to the specimen mis-setting but not to the collimator/slit misalignment. On the other hand, the defocusing method is sensitive to the collimator/slit misalignment but not to the specimen mis-setting.