A core molding machine which can be made smaller while having a favorable core sand filling property is provided. The machine comprises a core box having a pair of laterally separable dies and a sand filling device, having a blow head disposed under the core box, for filling the core box with core sand directed upward from the blow head; the blow head having a sand blow chamber for guiding the core sand to the core box while being connected to the core box and a sand storage chamber communicating with the sand blow chamber; the sand filling device having a compressed air supply unit for supplying a compressed air for blowing the core sand into the core box and an aeration air supply unit for supplying an aeration air for floating and fluidizing the core sand within the sand blow chamber.