There is provided a polarization maintaining optical fiber coupler and a method of manufacturing this polarization maintaining optical fiber coupler in which manufacturing is simplified and excess loss is reduced. A polarization maintaining optical fiber coupler is provided in which, in at least one of the polarization maintaining optical fibers forming the fused and extended portion, the ratio of the [diameter of the core/the diameter of the cladding] or [the distance between the two stress applying portions/the diameter of the cladding] is greater than the ration of the [diameter of the core/the diameter of the cladding] or [the distance between the two stress applying portions/the diameter of the cladding in the portions of the polarization maintaining optical fibers that do not form the fused and extended portion]. In addition, in this polarization maintaining optical fiber coupler, in the fused and extended portion, the stress applying portions are enveloped by the cladding. Moreover, polarization maintaining optical fibers are used in which the distance between adjacent outer circumferences of the two stress applying portions is 20 .mu.m or more.