The present invention relates to an MCF with a structure for enabling an alignment work -with higher accuracy. The MCF has a plurality of cores and a cladding. An outer peripheral shape of the cladding in a cross section of the MCF includes a circumferential portion forming a circumference coincident with an outer periphery of the MCF, and a cut portion. The cut portion has a bottom portion and two contact portions provided on both sides of the bottom portion and projecting from the bottom portion. When a side face of the MCF is viewed, the two contact portions have flattened faces and the flattened faces o f the two contact portions extend along a longitudinal direction of the MCF with the bottom portion in between.
