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Over four thousands of exoplanets have been found to date. To understand the formation mechanisms of these diverse exoplanets, it is essential to unveil the detailed physical properties of these exoplanets by various methods, including high-precision transit photometry from the ground. So far two observing techniques have succeeded in achieving high-precision photometry from the ground; one is defocusing and the other is using optical diffusers. Diffusers spread light from stars over many pixels and stabilize the top-hat like point spread function (PSF), reducing systematic noises in photometric observations. In addition to it, diffusers enable us to use longer exposure times, which reduces atmospheric scintillation noises. We have developed diffuser units and installed them to the optical three-band imager MuSCAT. Each diffuser unit can store two types of diffusers with different opening angles, which allows us to change the strength of scatter of light from stars. We installed the diffuser units to MuSCAT in July 2019 and carried out on-sky examination. We observed out of transit (oot) phase of 11 planet-hosting stars alternatively with the following three configurations: with diffusers, without diffusers and with onfocus, and without diffusers and with defocus. From these observations, we confirmed that diffusers stabilized PSF and peak counts of stars. Throughput of the diffusers are measured to be about 93%. In addition, with diffusers, we succeeded in observing 55 Cnc, which is too bright (V=5.4) to observe without diffusers. We achieved the photometric precisions of 426, 641, and 783 ppm per 1 minute, or 188, 221, and 196 ppm per 5 minutes, in g', r', and zs-band, respectively.
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