To provide a winding shaft structure in a winding shaft device, which allows offset of a plurality of shaft members when a wind-up shaft is formed of the shaft members connected together in series, and effectively transmits rotational force of the shaft members.

According to the winding shaft structure in the winding shaft device, the wind-up shaft 1 for winding-up and winding-off a shutter curtain as a curtain member, is formed by axially connecting the plurality of shaft members 1A, and the mutually adjacent shaft members 1A has an Oldham coupling 20 interposed therebetween, as an offset shaft rotational force transmitting means. Therefore, the Oldham coupling 20 functions to connect the mutually adjacent shaft members 1A together, and a floating cam 23 having linear projections 23A, 23B slidably engageable with grooves 21A, 22A of coupling main bodies 21, 22, respectively, performs floating motion, to thereby transmit the rotational force between the shaft members 1A containing offset shafts.