hello,i want to visit beijing before going to lhasa,is there any locker in Train St. to keep luggage

i am going to lhasa from beijing,i will reach beijing on the morning of the day of departure so i want visit beijing and see some places,but i am worried i dont have any place to keep my luggage on that time,so i would like to know if there is any locker in train station where we can keep our luggage safely,or any place like that.....thanx for your help..