The aim of the study is to investigate the effect of roflumilast taken orally together with low dose inhaled corticosteroids on lung function. Roflumilast will be administered at one dose level once daily together with inhaled corticosteroids at one dose level twice daily. The study duration consists of a baseline period (2 to 6 weeks) and a treatment period (24 weeks). The study will provide further data on safety, tolerability, and effectiveness of roflumilast.