  We study constraints from perturbativity and vacuum stability as well as the
EWPD in the type II seesaw model. As a result, we can put stringent limits on
the Higgs triplet couplings depending on the cut-off scale. The EWPD tightly
constrain the Higgs triplet mass splitting to be smaller than about 40 GeV.
Analyzing the Higgs-to-diphoton rate in the allowed parameter region, we show
how much it can deviate from the Standard Model prediction for specific
parameter points.
