In order to provide a wiring board comprising a magnetic material effective in suppressing spurious radiation in semiconductor devices and electronic circuits and the like that operate at high speeds, a wiring board (15) comprises an insulative base material (17), conductor patterns (19a to 19f) formed thereon, and magnetic thin films (21a to 21f) formed on the conductor patterns (19a to 19f. The magnetic thin film is configured of a magnetic loss material represented by M—X—Y, where M is at least one of Fe, Co, and Ni, X is at least one element other than M or Y, and Y is at least one of F, N, and O, the maximum value "max of the loss factor " that is an imaginary component in the complex permeability characteristic of the magnetic loss material exists within a frequency range of 100 MHz to 10 GHz, and a relative bandwidth bwr is not greater than 200% or not smaller than 150% where the relative bandwidth bwr is obtained by extracting a frequency bandwidth between two frequencies at which the value of " is 50% of the maximum "_max and normalizing the frequency bandwidth at the center frequency thereof.