To provide a waterproof battery for a film unit with lens with waterproof structure applied, without changing structure of conventional film unit with lens.

The waterproof battery is composed of a columnar power source battery 50 having a positive electrode 50a and a negative electrode 50b, a cylindrical battery case 51 wrapping up the power source battery 50, a positive electrode contact piece 52 contacting the positive electrode 50a of the power source battery 50 and a positive electrode contact piece 53 contacting the negative electrode 50b of the power source battery 50, exposed respectively to both ends of the battery case 51. The power source battery 50 is sealed watertight in the space surrounded by the battery case 51, the positive electrode contact piece 52 and the negative electrode contact piece 53. In addition, the power source battery 50 is a AAA battery, whose outside dimension constituted by the battery case and the pair of electrode contact pieces are almost same as that of a AA battery.