Unable to show string that have converted from shift-jis to utf8 (Only on Device)

Hi there.

I'm now testing about converting encoding.
It means...

1.Get shift-jis html text from web.
2.Convert to utf8 in code.
3.Show that on GUI.Label.

my c# script is...
==========================================================
using UnityEngine;
using System.Collections;
using System.IO;
using System.Collections.Generic;
using System.Text; //Encoding
using System.Text.RegularExpressions;

public class getwww : MonoBehaviour {
public GameObject cube;
//sjis page
string url="http://www.metro.tokyo.jp/INET/OSHIRASE/2014/08/20o8e200.htm";
private string str;

void Start () {
StartCoroutine(getURL());
}

IEnumerator getURL(){
WWW www=new WWW(url);
yield return www;
// str=sjisToUtf(www);
str=www.text;
}

// Update is called once per frame
void Update () {
if(Input.GetMouseButtonDown(0)){
Instantiate(cube,transform.position,transform.rotation);
}
}
void OnGUI(){
GUI.Label(new Rect(0,0,300,500),str);
}

public string sjisToUtf(WWW www){
byte[] bytesData=Encoding.Convert(Encoding.GetEncoding(932),Encoding.UTF8,www.bytes);
string utfstr= Encoding.GetEncoding("UTF-8").GetString(bytesData);
return utfstr;
}
}
=========================================================
Results are...

1."sjisToUtf" unable on editor
>> views garbled text but it's correct text.
2."sjisToUtf" enable on editor
>> views corrected text.
3."sjisToUtf" unable on Debice
>> views garbled text but it's correct text.
and it's same with 1.
4."sjisToUtf" enable on Device
No views with no error.
But application operate normally.

I uploaded 1.～4. screenshots.
What's wrong or any suggestions?

 

I reported now.
but I could'nt know what is case number.
You know Alex?

 

Ooh,I got mail now lol
Case number is 626398.