A battery condition estimation device estimates a pre-restart voltage drop amount ΔVjh+ΔVbn of a battery mounted to a vehicle during period T1 to T2 from initiation of an engine stop until initiation of an engine restart based on detection values regarding the battery condition. The device estimates a voltage drop amount ΔVst during period T3 from initiation of the engine restart until completion of the engine restart based on the detection values regarding the battery condition. The device finally estimates a minimum voltage of the battery during period T1 to T3 from the initiation of the engine stop until the completion of the engine restart based on a voltage detection value Vj0 before the engine stop, the pre-restart voltage drop amount ΔVjh+ΔVbn, and the voltage drop amount ΔVst.