BOL:
BULK INSERT ['database_name'.] [ 'owner' ] 'table_name' FROM 'data_file'
WITH KEEPIDENTITY
KEEPIDENTITY
Specifies that the values for an identity column are present in the file imported. If KEEPIDENTITY is not given, the identity values for this column in the data file imported are ignored, and SQL Server automatically assigns unique values based on the seed and increment values specified during table creation. If the data file does not contain values for the identity column in the table or view, use a format file to specify that the identity column in the table or view should be skipped when importing data; SQL Server automatically assigns unique values for the column. For more information, see DBCC CHECKIDENT.