An access device which is configured to access a write once recording device, said write once recording device having a write once memory allowing data writing only once and an address conversion control part configured to - divide the write once memory in units of fixed-length management units and manage the divided regions, - convert a logical address used in a communication with the access device into a physical region of each management unit on the write once memory, - when the access device issues a writing request, allocate an unrecorded region in the write once memory as a data recording region, and carry out an address conversion processing for relating a data recording region to a logical address designated by the access device in the writing request, - retain a correspondence relationship between a physical address and a logical address, and, in a case where the same logical address is related to a plurality of physical addresses, treats data stored in a region of the biggest-numbered physical address as valid data stored in a region of the logical address, said access device comprising: a file system control part configured to control data as a file on the basis of file system information constructed in a recording region in said write once recording device; characterized in that the access device further comprises a logical-physical empty capacity management part which is configured to: - obtain a remaining capacity on a logical address space from the file system information; - issue a command, to said write once recording device, to obtain a physical remaining capacity on a physical address space from the write once memory and receive said physical remaining capacity from said write once recording device,; - determine a smaller value, the physical remaining capacity obtained in response to the command or the remaining capacity on the logical address space obtained from the file system information, as an available recording capacity on the write once recording device. - divide the write once memory in units of fixed-length management units and manage the divided regions, - convert a logical address used in a communication with the access device into a physical region of each management unit on the write once memory, - when the access device issues a writing request, allocate an unrecorded region in the write once memory as a data recording region, and carry out an address conversion processing for relating a data recording region to a logical address designated by the access device in the writing request, - retain a correspondence relationship between a physical address and a logical address, and, in a case where the same logical address is related to a plurality of physical addresses, treats data stored in a region of the biggest-numbered physical address as valid data stored in a region of the logical address, a file system control part configured to control data as a file on the basis of file system information constructed in a recording region in said write once recording device; characterized in that the access device further comprises a logical-physical empty capacity management part which is configured to: - obtain a remaining capacity on a logical address space from the file system information; - issue a command, to said write once recording device, to obtain a physical remaining capacity on a physical address space from the write once memory and receive said physical remaining capacity from said write once recording device,; - determine a smaller value, the physical remaining capacity obtained in response to the command or the remaining capacity on the logical address space obtained from the file system information, as an available recording capacity on the write once recording device. - obtain a remaining capacity on a logical address space from the file system information; - issue a command, to said write once recording device, to obtain a physical remaining capacity on a physical address space from the write once memory and receive said physical remaining capacity from said write once recording device,; - determine a smaller value, the physical remaining capacity obtained in response to the command or the remaining capacity on the logical address space obtained from the file system information, as an available recording capacity on the write once recording device.