The Corona Australis Molecular Cloud has a head-tail shape with an elongated structure of ~5 pc from a dense gas of ~400 M<sub>?</sub>, and is known as a nearest (d=149 pc) low-mass cluster forming region. We analyzed ALMA Band 6 data of the actively star-forming head region of the cloud in order to understand the initial conditions of low-mass cluster formation.<br>
The ALMA ACA large mosaic data in C<sup>18</sup>O show complex internal morphology, i.e., a network of thin filamentary structures. We identified 91 filamentary structures (width ~1500 au) within the observed region (0.4 pc<sup>2</sup>) using the FilFinder algorithm. Some of the identified filamentary structures are confirmed to be really thin structures, which is also confirmed by partially available higher resolution data with the ALMA 12m array. Their typical line mass (0.7?7 M<sub>? </sub>pc<sup>-1</sup>) derived from the column density (0.5?5×10<sup>22</sup> cm<sup>-2</sup>) is much smaller than the critical line mass. Their typical linewidth is 1 km s<sup>-1</sup> with the inter-filaments velocity dispersion of ~ 1 km s<sup>-1</sup>, and thus they are in turbulent condition, implying external disturbance (e.g., HI shells or superbubble). Furthermore, only 10 filamentary structures are associated with young stellar objects (YSOs), while the cluster consists of 50 YSOs. These results suggest that most of the filamentary structures are transient, and do not fragment and form stars by gravitational instability. Recent high-resolution numerical MHD simulation reproduces the cloud structure very well, indicating that they are interpreted as results of the slow shock instabilities in converging gas flows with the ambipolar diffusion.