The nonequilibrium dynamicis of the superconductors has been intensively studied over decades. Among the viriety of nonequlibrium phenomena, the study of the collective dynamics of superconducting order parameter is of essential importance, as it provides deep insights into the properties of the order parameter. Recent developments of generating intense electromagnetic pulses in the terahertz (THz) frequency range have enabled the access to low energy collective modes without giving excess energy to the system. Particularly the amplitude fluctuation of the order parameter, referred to as the Higgs mode, has been observed in a conventional s-wave superconductor Nb1-x
N [1,2]. Its extension to unconventional d-wave superconductors is intriguing, whereas it has been nontrivial whether the Higgs mode in d-wave superconductors is observable or not.