A mechanical pencil is disclosed in which lead can be advanced in one of two ways; either automatically upon release of writing pressure on the pencil, or selectively manually by pressing inwardly against a side push button. The pencil includes an outer cylinder with a side pushing hole formed therein, and a side push button movably disposed in the side pushing hole. The side push button contacts a lever which is totally mounted within the outer cylinder and which contacts a lead advanced mechanism. Upon pressing in of the side push button, the lever is pivoted about its axis and caused to press downwardly against the lead advance mechanism to thereby cause advancement of a lead. Advancement of lead is also performed upon release of writing pressure of the pencil by way of a slider mechanism which is biased outwardly by way of a resilient member and which is forced outwardly by the resilient member upon release of writing pressure. This causes the slider to pull a lead forwardly to provide advancement thereof.