A mechanical seal device comprising: a rotational ring installed on a rotary shaft to integrally rotate with the rotary shaft and formed with a sealing surface (32, 33) on at least one of its surfaces in an axial direction; a stationary ring (41, 51) formed with a sealing surface (42, 53) to sealingly contact and slide with said sealing surface (32, 33) of said rotational ring; a rotational ring fixing portion for fixing said rotational ring to said rotary shaft; and a cover portion for containing said rotational ring and said stationary ring (41, 51) and for supporting said stationary ring (41, 51) so as to press the stationary ring(41, 51) axially movably in a direction of said rotational ring, characterized in that said rotational ring fixing portion comprises a sleeve fixturable on a surrounding surface of said rotary shaft, the sleeve having a rotational ring latching surface for latching together said rotational ring axially from outside or inside, and a through-bore of the sleeve in a radial direction for inserting a knock pin; and a rotational ring fixing collar fitted into said sleeve and arranged on axially inside or outside of the sleeve, the rotational ring fixing collar having a rotational ring latching surface for latching together said rotational ring from an opposing direction of said rotational ring latching surface of said sleeve, and a through-bore of the rotational ring fixing collar for inserting a knock pin in a radial direction communicating to said through-bore of said sleeve when the rotational ring fixing collar is fitted into said sleeve; and said rotational ring is axially sandwiched by said rotational ring latching surface of said sleeve and said rotational ring latching surface of said rotational ring fixing collar, and is fixed to said sleeve and said rotational ring fixing collar in a circumferential direction by engaging a knock pin inserted through said through-bores (216, 226) of the sleeve and the rotational ring fixing collar communicated with each other from an inner circumference side to a concave portion formed on the rotational ring. a rotational ring installed on a rotary shaft to integrally rotate with the rotary shaft and formed with a sealing surface (32, 33) on at least one of its surfaces in an axial direction; a stationary ring (41, 51) formed with a sealing surface (42, 53) to sealingly contact and slide with said sealing surface (32, 33) of said rotational ring; a rotational ring fixing portion for fixing said rotational ring to said rotary shaft; and a cover portion for containing said rotational ring and said stationary ring (41, 51) and for supporting said stationary ring (41, 51) so as to press the stationary ring(41, 51) axially movably in a direction of said rotational ring, characterized in that said rotational ring fixing portion comprises a sleeve fixturable on a surrounding surface of said rotary shaft, the sleeve having a rotational ring latching surface for latching together said rotational ring axially from outside or inside, and a through-bore of the sleeve in a radial direction for inserting a knock pin; and a rotational ring fixing collar fitted into said sleeve and arranged on axially inside or outside of the sleeve, the rotational ring fixing collar having a rotational ring latching surface for latching together said rotational ring from an opposing direction of said rotational ring latching surface of said sleeve, and a through-bore of the rotational ring fixing collar for inserting a knock pin in a radial direction communicating to said through-bore of said sleeve when the rotational ring fixing collar is fitted into said sleeve; and said rotational ring is axially sandwiched by said rotational ring latching surface of said sleeve and said rotational ring latching surface of said rotational ring fixing collar, and is fixed to said sleeve and said rotational ring fixing collar in a circumferential direction by engaging a knock pin inserted through said through-bores (216, 226) of the sleeve and the rotational ring fixing collar communicated with each other from an inner circumference side to a concave portion formed on the rotational ring.