In this study, we evaluated the relationship between the time variability of the transmission characteristics of multimode fiber (MMF) and laser linewidth. By varying the laser linewidth from 0.1kHz to 1.89THz, it is possible to grasp the tendency over a wide range, from narrow to ultra-wide linewidth. We were able to confirm that the time-varying characteristics of the frequency characteristics, which affect the MMF transmission characteristics, depend on the laser linewidth and time variability decreases with an increasing laser linewidth.