Temp db size is increasing not releasing space

Hi All

MS sql server 2008R2(RTM) STD 64 bit, Temp db size is continuously  increasing not releasing used up space , please suggest us what is the problem with my temp db ?

i  executed below query , please go through result.

DECLARE @runtime datetime
SET @runtime = GETDATE()

PRINT '-- sys.dm_db_file_space_used'
select CONVERT (varchar(30), @runtime, 121) AS runtime, SUM (user_object_reserved_page_count)*8 as usr_obj_kb,
SUM (internal_object_reserved_page_count)*8 as internal_obj_kb,
SUM (version_store_reserved_page_count)*8  as version_store_kb,
SUM (unallocated_extent_page_count)*8 as freespace_kb,
SUM (mixed_extent_page_count)*8 as mixedextent_kb
FROM sys.dm_db_file_space_usage
RAISERROR ('', 0, 1) WITH NOWAIT

ANS:

runtimeusr_obj_kb   internal_obj_kb version_store_kbfreespace_kbmixedextent_kb
2013-04-09 16:30:09.1871664956544384 11492736         4864

@@ When i restart the sql server services  temp db is minimal but with in few seconds again size is  growing high.