To provide a sheet having relatively uniform heat conductivity and heat releasing property, hardly accumulating heat in the application to a coil insulating material, and having an end rupture resistance by using a lining material making the end rupture resistance of a mica base material sheet layer than in the use of only glass cloth.

In this mica base material sheet, an inorganic powder more heat conductive than mica is included in at least an adhesive layer of a mica layer and the adhesive layer, a lining material consists of a cloth obtained by the of all or a part of a yarn consisting of an organic material, the yarn consisting of the organic material consists of a polyamide yarn or polyester yarn, and the mica layer preferably consists of mica paper, a synthetic fiber fibril of 5-50 pts.wt. to 100 pts.wt. of mica paper, and an inorganic powder of 5-50 pts.wt. to 100 pts.wt. of mica paper, which is more heat conductive than mica paper and having a particle size 5-50 μm. According to this, in winding work for mounting the sheet on a coil, the cutting is prevented to improve the productivity.