A ribbon cassette of which the type of ink ribbon accommodated in the ribbon cassette may be identified by detection switches arranged on the carriage of a thermal transfer printer, without using a plurality of types of ribbon cassette case which are different in shape. A ribbon cassette in which a simple construction is used to prevent sticking to each other of the ink ribbon and the guide roller immediately after printing. A ribbon cassette by which a stain on the recording sheet due to contact between the sheet and the ink ribbon at the time of printing operation may be prevented and the stability of running of the ink ribbon is improved. A thermal transfer printer in which: the stability of running of the ink ribbon may be improved; both hot peeling printing and cold peeling printing are possible in an excellent condition; and the consumption of the ink ribbon may be reduced.