We present the measurements of Faraday rotation for 477 pulsars observed by the Parkes 64m radio telescope and the Green Bank 100m radio telescope. Using these results, along with previous measurements for pulsars and extragalactic sources, we analyze the structure of the large-scale magnetic field in the Galactic disk. Comparisons of rotation measures of pulsars in the disk at different distances, as well as with rotation measures of background radio sources beyond the disk, reveal large-scale reversals of the field directions between the spiral arms and interarm regions. We develop a model for the disk magnetic field, which can reproduce not only these reversals but also the distribution of the observed rotation measures of background sources.