To provide a buffer access device of a disk reproducing device for managing a data area in a buffer RAM by a sector of a certain specified size, and having a data structure having fields suited to the sizes of plural data items in each sector.

This buffer access device manages a data area in a buffer RAM 6 by a sector of a certain specified size, and handles a data structure having fields suited to the sizes of plural data items in each sector. The data area is constituted of one kind of sector so that the address of the buffer RAM can be easily calculated from a sector number, sector length (fixed), field heading address (fixed) in the sector, and address in the field. The combination of the data items or the designation of a sub-address obtained by dividing unit data is operated in response to an instruction from a host CPU 8, and host transfer data can have various kinds of formats.