Abstract: A separator for fuel cells includes first channels that each include a first reduced region and a first enlarged region repeatedly located within a first general region. The first channels are configured to form a flow path of a reaction gas on a base plate. Second channels are arranged to be spaced apart from the first channels in parallel by a width-directional length of lands. The second channels include a second reduced region and a second enlarged region repeatedly located along the flow path within a second general region. The first enlarged region has the same shape as the second enlarged region. The first general region has the same cross-sectional area as the second general region. The first enlarged region and the second enlarged region each have a cross-sectional area corresponding to a cross-sectional area of the first general region.