This trial is conducted in Japan. The trial aims for comparison of the effect on glycaemic control of liraglutide in combination with sulphonylurea agent (SU) compared to SU monotherapy, as assessed by HbA1c after 24 weeks and 52 weeks in subjects with type 2 diabetes. Liraglutide will be compared to placebo, in combination with SU. Trial has a randomisation period of 24 weeks followed by a 28 week extension period, in total 52 weeks.