Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique that has been approved as a treatment of depression in patients that have not responded to a trial of one antidepressant medication. The investigators hypothesize that low frequency TMS exerts inhibitory effect on hyper excitable cortical state in patients with chronic insomnia and therefore is therapeutic. The investigators want to compare the change in insomnia scores between baseline and end of treatment in an open label trial with bifrontal low frequency TMS stimulation in 20 patients with primary insomnia using daily stimulation of 3 weeks (15 week days).