Al-Si Alloys which contain 0-2mass%Si were processed and machined by dry cutting in order to clarify effect of solid soluted Si on machinability of Al-Si alloy. In work material containing 0-1.5mass%Si, adhesion stacked on cutting edge widely and the surface roughness was increased with increasing the content of solid soluted Si. On the other hand, in the work material containing above 1.5mass%, adhesion on cutting edge spread thinly compared with other work materials and surface roughness was decreased. Moreover, eutectic Si was confirmed on machined surface in work material containing 2mass%Si. From those result, it was considered that solid soluted Si increased surface roughness.