Q: iPhone 4 model A1332 ios 7.1.2 keeps restarting itself. How to fix it ?

Hi Md. Abdur Rahman, 

Thanks for participating in the Apple Support Communities. 

If your iPhone 4 is restarting unexpectedly, there are a few things to do depending on how frequently this is happening. 

If it is restarting intermittently (from time to time), you may want to back up your data and restore the iPhone to factory settings:

Use iTunes to restore your iOS device to factory settings - Apple Support

If the same thing occurs, this article suggests contacting Apple Support for more help:

If your iOS device restarts, displays the Apple logo, or powers off while you're using it - Apple Support

Make sure your iOS device is up to date. If you still see this issue after updating, contact Apple Support.

Sincerely,

Jeremy