Thin battery

A method of producing a thin battery, comprising:

• a step for producing a battery body that includes an electricity generating element hermetically installed in an outer cover member made of a laminated film including a resin layer, an outer peripheral portion of the outer cover member being sealed;
• a step for preparing a spacer with a fixing portion by which the battery body is fixed to a predetermined position;
• a step for setting the spacer in an insert molding die in such a manner that the spacer is stacked on an outer peripheral portion of the battery body;
• and
• a step for carrying out an inserting molding by filling a material of elastic resin into a range that is provided at least around the fixing portion at the outer peripheral portion and includes a mutually overlapped portion between the outer peripheral portion and the spacer thereby to form in the range an elastic resin portion,
• wherein the spacer is formed, at a portion to be connected to the elastic resin portion, with a reinforced portion having a surface that faces against a direction in which an external force is applied from a direction parallel to a main face of said battery body.