A treadmill includes a tread platform having two longitudinal frame bars, a swing unit pivotally mounted at the bottom side of the tread platform, and two inclination angle adjustment blocks. Each inclination angle adjustment block has a core shaft defining an axis line, and a plurality of bearing faces connected to one another and respectively disposed in parallel to the axis line and adapted for selectively supporting the tread platform on the ground. Each bearing face defines with the axis line a respective different vertical distance. The core shafts of the inclination angle adjustment blocks are pivotally coupled to the swing unit to support the inclination angle adjustment blocks at an outer side relative to the longitudinal frame bars of the tread platform. Thus, the treadmill allows manual multi-angle adjustment of the angle of inclination of the tread platform.