Negative pressure type booster device

A negative pressure type booster device comprising:

• a booster shell formed by a front shell and a rear shell;
• a power piston that divides the interior of the booster shell into a negative pressure chamber and a variable pressure chamber and is movable in a front-back direction;
• and a tie rod bolt that hermetically penetrates through the booster shell and a movable partition wall included in the power piston and is fixed to the booster shell,
• the negative pressure chamber being configured to be formed between the front shell and the power piston and connected to a negative pressure source, and the variable pressure chamber being configured to be formed between the rear shell and the power piston and connected to the negative pressure chamber or atmosphere,
• wherein, in a penetration portion through which the tie rod bolt hermetically penetrates, the movable partition wall has a tubular guide portion that abuts against the tie rod bolt or an annular member provided on the front shell during forward movement of the power piston, and an annular sealing portion that is provided in the rear of the guide portion to interrupt the communication between the negative pressure chamber and the variable pressure chamber, and
• the guide portion or the tie rod bolt is provided with a communication portion for communicating the negative pressure chamber to a negative pressure chamber side space to which the front surface of the sealing portion exposes, even in a state in which the guide portion abuts against the annular member.