How to insert ampersand symbol.

Some product characteristics of my shop contain ampersand symbols (&).
As far as I understand, such symbols must be inserted by using special "escape" syntax, such as & a m p ;
However, after I save the article, & a m p ; is converted back to "&" without the special syntax.
As a result, WWW Validator says a error (see text below).
Is it correct way to keep ampersand in the text as it is without converting it to & amp ;?
If not, how shall I handle it?

TEXT OF THE ERROR
Line 737, Column 20: character "&" is the first character of a delimiter but occurred as data
Briggs & Stratton </span>

This message may appear in several cases:

- You tried to include the "<" character in your page: you should escape it as "<"
- You used an unescaped ampersand "&": this may be valid in some contexts, but it is recommended to use "&", which is always safe.
- Another possibility is that you forgot to close quotes in a previous tag.

Nicolas, noted, thanks.
It seems the reason is because I use RokPad by RocketTheme instead of common TinyMCE.