We have measured electrical resistance conductance across a single atomic step through a metallic monolayer on a crystal surface by using three independent methods that provide consistent values. The two were direct electrical conductivity measurements with monolithic microscopic four-point probes and four-tip scanning tunneling microscope probes. The other was scanning tunneling microscopy/spectroscopy observations on electron standing waves near step edges, combined with analyses based on the Landauer formula for 2D conductors. The present experimental results and the recent theoretical caluclations imply that the electron transport across an atomic step is fairly modeled as a tunneling process.