To provide a capacitor capable of having a larger capacity than a case where only a solid electrolyte is simply used as a dielectric material of the capacitor. The capacitor (1) includes a solid electrolytic body (3) and a plurality of electrodes (5, 7) which is formed on the solid electrolytic body (3) and disposed opposite to each other with the solid electrolytic body (3) interposed therebetween, and the solid electrolytic body (3) includes an oxide-based lithium ion conductive solid electrolyte as a base material and contains oxide particles formed of a part of elements configuring the base material.