What is this dash-like punctuation mark?

Here is a piece of text from 「ノルウェイの森」by Haruki Murakami:

この寮の唯一の問題点はその根本的なうさん臭さにあった。寮はあるきわめて右翼的な人物を中心とする正体不明の財団法人によって運営されており、その運営方針は――もちろん僕の目から見ればということだが――かなり奇妙に歪んだものだった。

How are these things before もちろん and かなり called and what function they serve?

Is it a mark equal to 、 or something informal like ~~~ and expressing a short speech pause in a middle of the sentence? In any case, what is its name?

Answer

It is called a "dash", ダッシュ in Japanese, according to this wikipage.

Several usages of the symbol are listed in the page. The usage here is to insert an extra explanation to the sentence (or word before the first dash). You can see that if you take off everything between the two dashes, the sentence is perfectly correct and meaningful. The portion between the two dashes is only to add an extra explanation that the statement is purely the writer's own opinion. You can treat it as a pair as bracket "()" here.