A self-refresh device, adopted in a memory array including a plurality of memory cells, includes a first word-line selecting module, which is enabled according to a first main-word-line signal, and a self-refresh controller. The first word-line selecting module includes a first selecting device, which selects a first word line according to a first word-line driving signal, and a second selecting device, which selects a second word line according to a second word-line driving signal. The self-refresh controller generates the first word-line driving signal, the second word-line driving signal, and the first main word-line signal to select one of the memory cells corresponding to the selected one of the first word line and the second word line for self-refreshing. When the first word line switches to the second word line, the self-refresh controller maintains the first main word-line signal at the same logic level.