We report on increasing the sensitivity of electro-optic sampling detection of terahertz pulses by using the effect of terahertz field enhancement in a tapered metallic waveguide. A thin Si prism, placed in the narrower section of the waveguide, is used to synchronize the enhanced terahertz field with the probe laser pulse propagating in a LiNbO3 crystal attached to the obliquely cut end of the waveguide. A 40-mu m-thick MgO-doped layer on the surface of LiNbO3 is used for guiding the probe pulse. The developed structure demonstrates a 20-fold higher detection sensitivity than a no-waveguide, Si-prism-coupled LiNbO3 crystal. (C) 2014 The Japan Society of Applied Physics.