Generally, systems, such as the pay-per-view TV, require secure multi-party communication. In these systems, group key is required, and members participate in and leave from party frequently, so that, group key materials of all members of the network must be updated. Therefore, an approach which tries to distribute a key materials effectively is proposed from Onen-Molva, the approach divides the members of the network into the two sub-groups according to the relative length in the period of the operation of the each member, and the approach uses FEC (Forward Error Correction) and an ARQ (Automatic Repeat reQuest) in the key update to the group of the long network-connection period. There are some issues in their proposal. When the communication quality is good, its efficiency is less, and there is an overhead in the bandwidth. Therefore, we propose an efficient group key distribution method using M-ary coding for a key message without using FEC and an ARQ, and transmitting this in parallel with the non-key message.