Our target is to support both small delay and small delay fluctuation of real-time traffic in IEEE802.11-based wireless LANs by using a decentralized manner. Several previous researches which aimed at supporting real-time traffic in IEEE802.11 wireless LANs developed decentralized control mechanisms achieving small delay of real-time traffic by differentiating real-time traffic from non-real-time traffic, but they cannot achieve small delay fluctuation because of the burst feature of the IEEE802.11 backoff mechanism. We propose a decentralized control mechanism for suppressing delay fluctuation in IEEE802.11-based wireless LANs. Our main proposal is a new backoff algorithm, called decentralized delay fluctuation control (DDFC), which can suppress delay fluctuation in a fully decentralized manner. DDFC can be easily used in IEEE802.11-based wireless LANs by replacing the current backoff algorithm of IEEE802.11 with DDFC. We examine the performance of DDFC, which is assumed to be used for real-time traffic in an IEEE802.11-based wireless LAN, by simulation. The results of computer simulation confirm that we can achieve not only small delay but also small delay fluctuation of real-time traffic in IEEE802.11-based wireless LANs by controlling real-time traffic according to DDFC.