  Dynamical properties are studied numerically for a variant of the Kondo model
with singlet and triplet crystalline electric field (CEF) levels where Kondo
and CEF singlets compete for the ground state. Using the continuous-time
quantum Monte Carlo method, we derive the $t$-matrix of conduction electrons
and dynamical susceptibilities of local electrons without encountering the
negative sign problem. When the CEF splitting is comparable to the Kondo
temperature, the dynamical response has only a quasi-elastic peak.
Nevertheless, the local single-particle spectrum shows an energy gap in strong
contrast with the ordinary Kondo model.
