The invention provides a wet type electrolytic capacitor. The capacitor includes a planar anode formed by compacted sintered powders, a cathode provided with a metal substrate coated with the electrochemically active material, and a working electrolyte for associating the planar anode with the cathode. The planar anode forms a concave portion on at least one surface thereof. The capacitor further includes at least one restraint device in contact with the concave portion and corresponding to the concave portion in shape. The concave portion of the planar anode can stabilize the planar anode by means of the restraint device. Therefore, the size of the capacitor is not increased at all.