To provide a blind plug device which can be surly fitted in a blind condition without the positional relationship underneath a manhole cover, and which is excellent in durability and cost.

A fastening nut 3 is screwed onto a male thread rod of a spindle 2 fitted in a body, and a split groove 14 is formed in the outer peripheral part 13 of the lower part of the body, one of wall surfaces of the split groove 14 serving as a normal rotation limiting surface 15 against which a fixing pawl 9 of the fastening nut 3 abuts during normal rotation, and the other of the wall surface of the split groove serving as a reverse rotation limiting surface 15 against which the fixing pawl abuts during reverse rotation. When the spindle 2 is rotated between the normal rotation limiting surface 15 and the reverse rotation limiting surface 16, the fastening nut 3 is rotated, integrally with the spindle 2, the fastening nut is rectilinearly moved along the spindle 2 after the pawl 9 abuts against the limiting surfaces 15 or 16.