Disclosed is a micro actuator capable of being formed in compact as a whole, such as 10 mm in diameter by diminishing a difference between a stroke distance of a moving member and an overall length, and by reducing a sectional area taken in a direction orthogonal to a stroke direction. The micro actuator includes: a spline shaft formed as a cylinder with a hollow part and having an axially extending slit opening; a spline nut fit-engaged with the spline shaft and axially guiding the spline shaft; a pair of end caps fixed to openings at both ends of the spline shaft; a magnet rod supported at both ends within the hollow part of the spline shaft by the end caps; and a forcer loosely fit-engaged with a periphery of the magnet rod within the hollow part of the spline shaft to constitute a linear motor together with the magnet rod and connected with the spline nut through the slit opening.