By asking this question the interviewer is trying to establish how committed you are to staying with the Company because if they are prepared to put the effort and expense into training you and teaching you all there is to know they won't look very favorably on someone who is using them just a stop-gap until 'something better comes along'.
You can start by telling that you want to learn as much as you can in this job and then grow in the same profession to a senior level in the same company where you can use and apply these skills and the knowledge that you gained in this position that you have applied for. This kind of answer will show the interviewer you mean business and you are there for the long haul and are prepared to build and grow with the Company.
Try to take a look at the job description and see what skills you might develop by being in this job, these can be used in forming a more appropriate and effective answer.