[Problem] To provide an apparatus for bonding separators in electrical devices wherein even if a unit that performs bonding using ultrasound is used in assembly-line equipment, the amount of space taken up by said equipment can be kept small. [Solution] The present invention is an apparatus 100 for bonding separators in electrical devices, which is used to bond a pair of separators 40 to each other so as to sandwich an electrode 20, provided with an oscillator 153 that generates ultrasonic oscillations; a booster 152 that amplifies the generated oscillations; a horn 151 that applies the amplified oscillations to the pair of separators so as to bond said separators to each other; and separator conveyance units 120, 130 that convey the pair of separators to a bonding position where the horn bonds said separators to each other, wherein the oscillator, the booster, and the horn are laid out in a plane that is parallel to the direction X in which the separators are conveyed and perpendicular to the surfaces of the separators, or the oscillator and the booster are laid out closer to the widthwise centers of the separators than the horn is when seen from a direction that is parallel to the direction in which the separators are conveyed.