Basin subsiding properties in a back-arc basin are clarified based on sequence stratigraphic analysis．Main focus is the Middle Miocene in Izumo area in Shimane Prefecture．We recognized 19 sedimentary facies and 7 depositional sequences．We also carried out sequence stratigraphic analysis for the Middle Miocene Iya district，which is located on 50 ㎞ east from lzumo area．However，the Middle Miocene of lzumo area and lya district is deposited in the same sedimentary basin．We recognized 8 sedimentary facies and 3 depositional sequences in Iya district．It is possible to estimate the intra-basinal subsiding difference between Izumo area and Iya district，based on the relative sea level curves of these area and district．The intra-basinal subsiding difference indicates that the local rapid subsiding occurs during the volcanic furious period．