Provided is a negative pressure type booster device, in which a diaphragm of a movable partition wall has, in a penetration portion through which a tie rod bolt hermetically penetrates, a tubular guide portion that abuts against an annular flange portion provided on the tie rod bolt during forward movement of a power piston, and an annular sealing portion that is provided in the rear of the guide portion to block communication between a negative pressure chamber and a variable pressure chamber. The guide portion is provided with a communication portion through which a negative pressure chamber side space exposed by the front surface of the sealing portion communicates with the negative pressure chamber, even in a state in which the guide portion abuts against the annular flange portion.