We demonstrate for the first time a high-speed parallel optical signal transmission using multi-channel optical axis converter having U-shape optical paths (AXC-U), which has been developed to apply to optical printed wiring board (OPWB). AXC-U developed here contains 4-channel multimode waveguides, which have vertical waveguides and 45-degree mirrors connected at both ends of horizontal waveguides using to form U-shape optical paths. The AXC-U accommodates VCSEL and PD arrays, which are surface-mounted on each end to perform optical coupling to vertical waveguides in a manner of passive alignment and flip-chip bonding. The waveguides in AXC-U have a horizontal waveguide length of 2 cm, a vertical waveguide length of 100 μm, a cross section of 40x40 μm, a numerical aperture of 0.25 and an insertion loss of less than 2.5 dB. We performed a parallel optical signal transmission experiment using this AXC-U and succeeded in 4-channel parallel transmission at a data rate of 10 Gb/s/ch.