I am sorry for the delay.
Thank you very much. Problem solved.
First.
I made the derived from UObject instead of from UBlueprint.
However, EventGraph(UbergraphPages?) cannot be accessed from MyClassInstance (derived from UObject), I created a MyClassBlueprint (derived from UBlueprint) separate from MyClassInstance.
(Maybe the interpretation is wrong.)
Next, I set UMyClassInstance::StaticClass to ParentClass in MyClassBlueprintFactory.
This way, when MyClassBlueprint is created in the editor, ParentClass becomes MyClassInstance and the class in BlueprintEditor becomes MyClassBlueprint.
As a result, I can call CustomEvent of Blueprint’s EventGraph in C++ through MyClassInstance at the execution of my own node.
thank you ｄ(・＿・)ｂ