Find visits who searched more than twice

To answer your quesiton, i am assuming searches which you are talking about is external searches coming from the search engines and not internal search inside your website.

I want to see the behaviors which users searched and came into my page with search engine, and go back to search engine and searched another page on my site and came.
Answer: You can try building a segment where search engine value is greater than 1, which means that people have used search engine in their respective visits more than once.

I want to prove the reason why [searches] are more than [visits] in my site.
Answer:Please double check whether you are looking into the internal search instance(people searching on your website) or external search instance( from search engines).

I looked into Flow report, Ad-hoc Analysis. chose one page and set segment with [Visits from Natural Search](Pre-Configured).
The first page's occurrences(metric) are similar to searches I find out another way.
In this case, can I regard next pages' values as seaches that users found first page and searched second page with search engine continuingly?
Answer: You had to take into account the navigation possibility also. People might be navigating to the next page through navigation also.

- we can think of second pages' [searches] values are from those session which generated when they searched and came into first page.
Answer: Yes we can but next page shows the values where people had landed after the first page immediately.This includes your suggested case as well.

Let me know if it helps you and you can mark it closed if it solves your query.

Thanks

Akhil