This invention is directed to a power supplier for use, for example, in a portable camera which includes a battery housing for accommodating a set of cylindrical batteries in parallel relationship with each other, and a battery door which is connected to the battery housing by means of a hinge so as to open an opening of the housing and to close the opening so as to axially depress the batteries. The batteries are located in the battery housing at two positions, i.e. one position relatively close to the hinge and the other position relatively remote from the hinge. The power supplier further includes a detector which is mounted on the bottom of the battery housing so as to operate when at least one battery located at the position remote from the hinge is depressed due to the battery closing operation and the batteries are connected to each other in series, and a switch which is mounted on the bottom of the battery housing so as to operate due to the operation of the detector to generate a signal indicating that the batteries have been connected to each other in series.