microsoft excel 2010 - how to get encode type of text file using vba

I would like to check encode type of text file is UTF-8 without bom or SHIFT-JIS.
Because I change to SHIFT-JIS if encode type is UTF-8 without bom.
So I want to get encode type of text file.
What is the best way for doing this?
Please explain.

Edit

Dim obj1 As Object, obj2 As Object
Set obj1 = CreateObject("ADODB.Stream")
Set obj2 = CreateObject("ADODB.Stream")
obj1.Type = 2
obj1.Charset = "UTF-8"
obj1.Open
obj1.LoadFromFile strLogFileName
obj1.Position = 0
obj2.Type = adTypeText
obj2.Charset = "Shift_JIS"
obj2.Open
obj1.CopyTo obj2
obj2.SaveToFile strLogFileName, 2
obj2.Close
obj1.Close
Set obj1 = Nothing
Set obj2 = Nothing

The above is Convert "UTF-8" to "Shift_JIS" Code.

I am developing read from text file and write into csv file.
Encode type of original text file is UTF-8.
When write UTF-8 encoded data into CSV, Japanese Characters can't be displayed correctly.
Therefore, convert encode type of text file before reading.
But that code is OK for only first time.
When read the same text file next time, error happens in writing process.
Because Japanese Characters of text file change abnormal character(eg:???)
when file have already been "Shift_JIS" is encoded to "Shift_JIS".
So I want to check encode type is "UTF-8" or not before converting.