A video data transmitting device 30 manages storage areas 31a, 31b of a memory card 31 by equally segmenting these storage areas into partitions whose capacities are equal to each other. Image data forming video data is stored piece by piece in each partition in the sequence from a head partition toward a tail partition. Then, the image data is overwritten sequentially from the oldest, whereby the storage areas 31a, 31b are always temporarily stored with N-pieces of image data starting from a point of the time when recording the image data and ending to a point of time tracing back for a predetermined period of time.