The invention relates to a curing accelerator for a curing resin obtained by reacting a phosphine compound (a) with a compound (b) having at least one halogen atom substituted on an aromatic ring and at least one proton atom which can be discharged, and subjecting the reaction product to dehydrohalogenation, a curing resin composition containing the curing accelerator, and an electronic component device having a device component encapsulated with the curing resin composition. The curing accelerator exhibits superior curability under moisture absorption, flow properties, reflow cracking resistance and high-temperature storage characteristics.