  We revisit a scenario with an enhanced top yukawa coupling in vector-like
quark (VLQ) models, where the top yukawa coupling is larger than the standard
model value and the lightest VLQ has a negative yukawa coupling. We find that
the parameter space satisfying the LHC bounds of the Higgs signal strengths
consistently with the precision measurements is rather wide. Because the
Lagrangian parameters of the yukawa couplings are large, such scenario can be
realized in some strongly interacting theories. It also turns out that there is
a noticeable relation between the contributions of the triangle and box
diagrams in the $gg \to hh$ process by using the lowest order of the $1/M$
expansion where $M$ is the heavy mass running in the loops.
