A movable fixing structure is used for causing the first casing to be combined with or detached from the second casing along a first axial direction. The movable fixing structure includes a blocking component, a locating element and a limiting element. The blocking component is movably disposed on the first casing along a second axial direction. The blocking component is used for moving between a first position and a second position. The locating element has a first locating portion and a second locating portion. The locating element is disposed on the first casing and is used for moving between a third and a fourth position along a third axial direction. The limiting element is disposed on the second casing and is used for interfering with the second locating portion on the first axial direction.