A production method efficiently produces a box sealed type solid electrolytic capacitor in which a capacitor element is accommodated in a box-shaped case. The method includes a step of preparing a bottom wall substrate having bottom walls. A step forms cathode anode circuit patterns on the bottom wall substrate. A step prepares a peripheral side wall substrate having peripheral side walls. A step prepares a peripheral side wall substrate in which a plurality of through-holes are provided that correspond to plurality of bottom wall structural portions. A step fixes a capacitor element to each bottom wall structural portion of the bottom wall substrate. A step obtains a capacitor continuous member in which a plurality of capacitor structural portions structuring a solid electrolytic capacitor by attaching an upper lid substrate on the peripheral side wall substrate. A step obtains a plurality of solid electrolytic capacitors by cutting the capacitor continuous member.