The present invention provides a planar lightwave circuit platform and its method for manufacturing by which the characteristics of the planar lightwave circuit become stable. In a planar lightwave circuit platform comprising quartz-based lower cladding layer (2), height adjusting layer (3), core layer (4), and upper cladding layer (5) formed in order on substrate (1), wherein the glass softening temperature of the height adjusting layer (3) is set to be higher than the glass softening temperatures and the temperatures for transparent-vitrification of the core layer (4) and upper cladding layer (5).