An omnidirectional camera comprises a camera having an image pickup element for acquiring a digital image, an image data processing device for compressing signals from the camera and for converting the signal to an image signal, and an external memory. The image data processing device has a signal processing unit, a writing changeover unit, a set of two first internal memories, a signal compensation unit, a data conversion unit, a third internal memory for temporarily storing the outputted data, and an input/output control unit for controlling the input/output of the data between the third internal memory and the external memory. The writing changeover unit accumulates signals outputted from the signal processing unit in one of the first internal memories until the signals are accumulated to a predetermined amount, and then, the writing changeover unit changes the destination of accumulation and repeatedly accumulates in the other first internal memory.