The Japan Atomic Energy Agency's accelerator-driven subcritical system (JAEA-ADS) proposes the reduction of nuclear waste through the transmutation of minor actinides. The JAEA-ADS drives a 30-MW proton beam to a spallation target to produce neutrons for a subcritical 800-MWth reactor. The beam must be transported from the end of the linear accelerator (linac) to the target located inside the reactor core with high beam power stability and low peak density to ensure beam window integrity, which is a primary concern for the ADS project. Additionally, the design of the beam transport to the target (BTT) must be compatible with the established reactor design, and the elements that comprise the BTT must facilitate the maintenance and replacement of the fuel and the beam window. To this end, a robust-compact BTT design was developed through massive multiparticle simulations. First, the beam optics was optimized to guarantee beam window feasibility requirements by providing a low peak density of less than 0.3 mu A/mm(2). Then, beam stability was evaluated and improved by a simultaneous application of input beam and element errors. The input beam errors were based on the beam degradation obtained by implementing fast fault compensation in the linac, which is a key strategy to attain high-reliability operation. The results show that the BTT design fulfills reactor and beam window requirements for JAEA-ADS.