The mechanical-collimation imaging is the most mature technology in prompt gamma (PG) imagingwhich is considered the most promising technology for beam range verification in proton therapy. Thepurpose of the present study is to compare the performances of two mechanical-collimation PG cameras,knife-edge (KE) camera and multi-slit (MS) camera. For this, the PG cameras were modeled by Geant4Monte Carlo code, and the performances of the cameras were compared for imaginary point and linesources and for proton beams incident on a cylindrical PMMA phantom. From the simulation results, theKE camera was found to show higher counting efficiency than the MS camera, being able to estimate thebeam range even for 107 protons. Our results, however, confirmed that in order to estimate the beamrange correctly, the KE camera should be aligned, at least approximately, to the location of the protonbeam range. The MS camera was found to show lower efficiency, being able to estimate the beam rangecorrectly only when the number of the protons is at least 108. For enough number of protons, however,the MS camera estimated the beam range correctly, errors being less than 1.2 mm, regardless of thelocation of the camera