The present invention provides a microstrip line for a printed wiring board such as a flexible printed wiring board which includes a sandwiched thin insulating layer and cannot use a solid grounding conductor, the microstrip line being such that shape of grounding conductors relative to signal lines remains unchanged even in the presence of a curved shape and that overlapping areas of signal lines and grounding conductors located opposite to each other remain unchanged even in case of exposure misalignment or stack misalignment. A printed wiring board with a microstrip line structure in which signal lines are curved include wire-type grounding conductors 5, 9, 12, 15, 19, or 26 located across an insulating layer 3, 10, or 13 from the signal lines 4, 6, 8, 11, 14, 18, or 25, characterized in that wiring pitch of the grounding conductors is 1/n of width of the signal lines (where n is a natural number of 1 or 2).