  We study gravitational waves from the first-order electroweak phase
transition in the $SU(N_c)$ gauge theory with $N_f/N_c\gg 1$ ("large $N_f$
QCD") as a candidate for the walking technicolor, which is modeled by the
$U(N_f)\times U(N_f)$ linear sigma model with classical scale symmetry (without
mass term), particularly for $N_f=8$ ("one-family model"). This model exhibits
spontaneous breaking of the scale symmetry as well as the $U(N_f)\times U(N_f)$
radiatively through the Coleman-Weinberg mechanism $\grave{a}$ la
Gildener-Weinberg, thus giving rise to a light pseudo dilaton (techni-dilaton)
to be identified with the 125 GeV Higgs. This model possess a strong
first-order electroweak phase transition due to the resultant Coleman-Weinberg
type potential. We estimate the bubble nucleation that exhibits an ultra
supercooling and then the signal for a stochastic gravitational wave produced
via the strong first-order electroweak phase transition. We show that the
amplitude can be reached to the expected sensitivities of the LISA.
