A mechanical pencil comprising a lead feeding mechanism including a receiving part and an interference part, and a lead cartridge for storing leads, the lead cartridge being capable of being detachably connected to the receiving part of the lead feeding mechanism to supply the leads one by one to the lead feeding mechanism, said lead cartridge comprising: a case (12, 12'); a tank part formed inside the case (12, 12') for storing the leads; a tip end connection part formed at a tip end part of the case (12, 12') and capable of being detachably fitted with the receiving part of the lead feeding mechanism; a lead port formed between the tank part and the tip end connection part in the case (12, 12') to allow one of the leads in the tank part to pass therethrough from the tank part; and a swing cover arranged in the case (12, 12') so as to be swingable between a closing position where the swing cover closes the lead port, and an opening position where the swing cover opens the lead port; the swing cover being biased in a swing direction from the opening position to the closing position but is adapted to be swung from the closing position to the opening position by the interference part when the tip end connection part is fitted with the receiving part; and the swing cover being mounted in a side opening formed in a side part of the case (12, 12') and extending in an axial direction at least on the tank part, wherein on the closing position, at least a part of the swing cover is arranged inward from the side opening in the tank part so that the swing cover closes the lead port, whereas on the opening position, the swing cover aligns with the side opening so that the swing cover opens the lead port; characterized in that the swing cover has a protrusion formed thereon, the protrusion being positioned posterior to the lead port when the swing cover is on the closing position, so that the swing cover prevents a lead in the tank part from aligning with the lead port. a case (12, 12'); a tank part formed inside the case (12, 12') for storing the leads; a tip end connection part formed at a tip end part of the case (12, 12') and capable of being detachably fitted with the receiving part of the lead feeding mechanism; a lead port formed between the tank part and the tip end connection part in the case (12, 12') to allow one of the leads in the tank part to pass therethrough from the tank part; and a swing cover arranged in the case (12, 12') so as to be swingable between a closing position where the swing cover closes the lead port, and an opening position where the swing cover opens the lead port; the swing cover being biased in a swing direction from the opening position to the closing position but is adapted to be swung from the closing position to the opening position by the interference part when the tip end connection part is fitted with the receiving part; and the swing cover being mounted in a side opening formed in a side part of the case (12, 12') and extending in an axial direction at least on the tank part, wherein on the closing position, at least a part of the swing cover is arranged inward from the side opening in the tank part so that the swing cover closes the lead port, whereas on the opening position, the swing cover aligns with the side opening so that the swing cover opens the lead port; characterized in that the swing cover has a protrusion formed thereon, the protrusion being positioned posterior to the lead port when the swing cover is on the closing position, so that the swing cover prevents a lead in the tank part from aligning with the lead port.