Patent ID: 7362993

Claim:
A transfer device comprising: a belt device that moves a belt member endlessly by rotating a driving roller while the belt member is spanned by spanning members, wherein the driving roller is one of a plurality of the spanning members; and a plurality of transfer units that transfer in a superimposing manner, visible images carried on corresponding image carriers, onto any one of an obverse face of the belt member and a recording member held on the belt member, wherein the transfer units are arranged inside a loop of the belt member, each the transfer unit being placed opposite to one of a plurality of the image carriers that are arranged equidistantly outside the loop of the belt member, and at a pitch identical to a pitch at which the image carriers are arranged, wherein the driving roller satisfies a condition “(R 4 -R 3 )π×(st−1)×pt/(R 3 ×π×2)≦0.15 millimeter”, where R 3 is a diameter of the driving roller under an environment of minimum temperature and minimum moisture in a use environment range designed, R 4 is a diameter of the driving roller under an environment of maximum temperature and maximum moisture in the use environment range designed, pt is an arrangement pitch of the transfer units, st is a total number of the transfer units, and π is the circle ratio pi.