We investigated the inertial focusing in triangular channel under various conditions. Configuration of focusing positions were altered depending on a/H (a=particle diameter, H=hydraulic diameter) and Re. In addition to the diversity of focusing configuration in a triangular channel, a microchannel with varying cross-sectional shapes for manipulation of accessible focusing positions is applied to particle separation based on particle size. Regulation of triangular channel dimension and Reynolds number enables tuning of the separation size.