A polycarbonate foam that is a thermoplastic resin foam suitable for a backlight or a lighting box of an electric signboard, a luminaire, a display, and the like, has both high optical reflectivity and shape-retaining property, and has a short production cycle time. A polycarbonate foam contains a polycarbonate (A) and a fluorinated polycarbonate (B) and has a plurality of pores with a mean bubble diameter of 10 micrometers or less within. The foam is manufactured by a manufacturing method including holding a resin sheet containing the polycarbonate (A) and the fluorinated polycarbonate (B) in a pressurized inert gas atmosphere and incorporating the inert gas into the resin sheet, and heating the resin sheet incorporated with the inert gas to a temperature equal to or higher than a softening temperature of the polycarbonate under ambient pressure and foaming the resin sheet.