A forming die assembly for microcomponents includes a forming die, a plunger, and a punch. The forming die is formed with a cavity, a storage portion for storing a raw material with a metal powder and a binder having plasticity, and a punch hole that connects the cavity and the storage portion so as to form a gate therebetween. The plunger is formed so as to be slidably inserted into the storage portion and to fill the raw material stored in the storage portion into the cavity through the punch hole. The punch is slidably inserted into the plunger in the sliding direction of the plunger and opens and closes the gate by reciprocatory sliding. The punch closes the gate and compresses the raw material in the cavity into a green compact by sliding in the direction of the cavity.