A metallic base gasket coated with elastic membrane having an outer sealing portion for sealing an outer circumference of a refrigerant compressor and an inner sealing portion for sealing boundaries between high and low pressure regions within the compressor, the outer and inner sealing portions being formed in an elastically deformable ridge, and at least one section of the ridge of the inner sealing portion being trifurcatedly connected to a portion of the ridge of the outer sealing portion to have a geometrical arrangement in which apex lines of the connected three ridges are equiangularly spaced apart from one another with respect to the center of the trifurcated connection of the ridges. The gasket may have an extended flat or curved face portion at the trifurcatedly connected ridges to permit the apexes of the connected ridges lie in the extended flat or curved face portion.