Study was performed on the stick-slip phenomenon between the Muscovite mica and a cantilever tip. An atomic force/lateral force microscope with an optical lever deflection method was used, which detects the deflection and the torsion of the cantilever simultaneously. We observed the square-wave behavior across the scan direction, but the well-known sawtooth behavior due to the stick-slip motion of the tip along the scan direction. It is found that the square-wave and sawtooth behaviors were synchronized with each other. To explain these behaviors, we propose two-dimensional stick-slip model. In this model, the periodicity of the stick point is the same of that of the lattice structure of the mica surface, so that the tip apex takes a zig-zag walk along the scan.