When answering questions like this, be positive and explain that you are moving towards something new, not away from something old. Discuss your desire to be challenged and the rewards you will get by helping a new organization achieve its objectives. Also, talk about the opportunity to improve yourself by acquiring new skills and experiences in a new position.

"While I enjoy the work I do and the organization I am associated with, I'm always looking for new challenges and opportunities to develop myself. While researching this job, I discovered that your organization would benefit from my experience, skills, and expertise to address your current challenges. I also noted that this role would expose me to opportunities to learn new skills, develop new relationships, and improve my overall qualifications. Finally, this job represents an increase in responsibility which I am always seeking."