if admin is logged in

We know, that is_admin() checks if current URL belongs to DASHBOARD (BUT it doenst check whether user is ADMIN).

So, I use this function to detect if administrator is logged in wordpress:

function is_admin_user(){
  require_once(ABSPATH.'wp-includes/pluggable.php'); return current_user_can('create_users'); //or 'manage_options'
}

however, that is not ideal solution. Does there exist any built-in function, like wp_is_administrator()?

current_user_can will accept a role name but, sadly, the behavior with roles is not entirely consistent.

The following should work and is simpler than what you have, by a little bit.

$current_user = wp_get_current_user();
if (user_can( $current_user, 'administrator' )) {
  // user is an admin
}