Because a massively parallel computer processes vast amounts of data and generates many access requests from multiple processors simultaneously, parallel secondary storage requires large capacity and high concurrency. One effective method of implementation of such secondary storage is to use disk arrays which have multiple disks connected in parallel. In this paper, we propose a parallel file access method named DECODE (dynamic express changing of data entry) in which load balancing of each disk is achieved by dynamic determination of the write data position. For resolution of the problem of data fragmentation which is caused by the relocation of data during a write process, the concept of "Equivalent Area" is introduced. We have performed a preliminary performance evaluation using software simulation under various access statuses by changing the access pattern, access size and stripe size and confirmed the effectiveness of load balancing with this method.