A hole-assisted holey fiber is provided. The holey fiber includes a core region; a cladding region around the core region, and a plurality of holes in the cladding region around the core region. The core region has a higher refractive index than that of the cladding region. The holes form an inner hole layer and an outer hole layer, and the inner hole layer has the same number of holes as the number of the holes in the outer hole layer. The outer layer holes are provided in locations in which inner holes are absent when viewed from the center of the core region, and holes defining the same layer have the same diameter. A distance .LAMBDA..sub.1 from a center of the core region to a center of an inner hole and a distance .LAMBDA..sub.2 from the center of the core region to a center of an outer hole satisfy the relationship .LAMBDA..sub.1<.LAMBDA..sub.2, and a diameter d.sub.1 of an inner hole and a diameter d.sub.2 of an outer hole satisfy the relationship d.sub.1.gtoreq.d.sub.2.