The tunneling current through a junction array consisting of a scanning tun
neling microscope tip and a granular film is studied both theoretically and
experimentally. When the tunnel resistance between the tip and a granule o
n the surface is much larger than those between granules, a bottleneck of t
he tunneling current is created in the array and the Coulomb staircase (CS)
appears in the I-V curve at room temperature. It is shown that the period
of the CS is given by the capacitance at the bottleneck even though a granu
lar film consists of many tunnel junctions with different capacitances. Our
study provides a possibility for single-electron-spin-electronic devices a
t room temperature.