Apache doesn't show me PHP errors

edit

I already change /etc/php.ini configurations... to be honest, I just erase the ; at beginning of lines as bellow

 display_errors
   Default Value: On
;   Development Value: On
;   Production Value: Off

 display_startup_errors
   Default Value: Off
;   Development Value: On
;   Production Value: Off

 error_reporting
   Default Value: E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED
;   Development Value: E_ALL
;   Production Value: E_ALL & ~E_DEPRECATED & ~E_STRICT

 html_errors
   Default Value: On
;   Development Value: On
;   Production value: On

 log_errors
   Default Value: On
;   Development Value: On
;   Production Value: On

Even my changes, when I run some php wrong php script the page remains either entirely blank or in some parts of that, but no errors messages are displayed. How can I turn it on?

Thanks in advance :)