To provide a cylindrical armature core structure for a linear motor capable of improving assembling precision and facilitating assembly of an armature by reducing the time required for assembling a thin plate constituting a core.

This cylindrical armature for the linear motor is structured by fitting the cylindrical core 4 formed by layering the C-shaped sheet plate made of a plurality of ferromagntic materials on a non-magnetic shaft 3, and by winding an armature winding on the outer periphery of the core 4 along the axial direction. The shaft 3 is formed with a positioning groove 3A so as to be fitted to the groove 4A of the C-shaped A core 4, and a rod-shaped core fixing member 9 is fitted into the groove 4A of the core 4 and the groove 3A of the shaft 3.