A memory device (1) includes at least a first semiconductor region (100) having a length, a first surface, and a cross section surrounded by the first surface, a memory means (300) provided on the first surface, and a gate (400) provided on the memory means (300), and an equivalent sectional radius of the cross section of the first semiconductor region (100) is set to be equal to or smaller than an equivalent silicon oxide film thickness of the memory means (300) to realize low program voltage. The equivalent sectional radius r of the cross section is set to be 10 nm or less and the gate length is set to be 20 nm or less so that multi-level interval converted to gate voltage becomes a specific value which can be identified under the room temperature.