  Walking technicolor theory attempts to realize electroweak symmetry breaking
as the spontaneous chiral symmetry breakdown caused by the gauge dynamics with
slowly varying gauge coupling constant and large mass anomalous dimension.
Many-flavor QCD is one of the candidates owning these features. We focus on the
SU(3) gauge theory with ten flavors of massless fermions in the fundamental
representation, and compute the gauge coupling constant in the Schr\"odinger
functional scheme. Numerical simulation is performed with $O(a)$-unimproved
lattice action, and the continuum limit is taken in linear in lattice spacing.
We observe evidence that this theory possesses an infrared fixed point.
