To provide a warm water producing device of a simple constitution capable of producing warm water by utilizing combustion heat of a pellet stove, and to provide a soil warming system capable of warming the soil in a vinyl greenhouse by using the warm water producing device.

This warm water producing device 220 includes: a tank body 230 constituted engageably with a pellet stove body 2 of the pellet stove, and having a heat transfer face section 236 receiving heat from the pellet stove body 2; a water supply section 240 disposed on the tank body 230 and introducing the water to the inside of the tank body 230; and draining sections 250, 251 disposed on the tank body 230 and draining warm water to the external of the tank body 230.