Concerning medical treatments for adult attention-deficit/hyperactivity disorder (AD/HD), case reports have gradually been accumulating on the efficacy of psychostimulants such as methylphenidate and amphetamine and selective noradrenaline reuptake inhibitors such as atomoxetine. However, patients intolerant to psychostimulants currently have a very limited range of treatments available to them. Here, we report a case of an adult AD/HD patient whose inattention and hyperactivity were remarkably alleviated by milnacipran, a serotonin noradrenaline reuptake inhibitor. Milnacipran has fewer side effects than comparable drugs, and we believe it could be developed into a good curative treatment for AD/HD in the future.