Device for preventing the turbo-charger from over-running

The invention relates to a device for preventing the turbo-charger (3) from over-running, wherein an actuator (5) is arranged in a by-pass (26) bypassing a turbine (31) of the turbo-charger (3) and operates a waste gate valve (9). The actuator (5) has apositive pressure chamber (51a) communicated, via a boost pipe (6), with an intake air passage (24) downstream of a compressor (32) and a negative pressure chamber (51b) communicated with a source (7) of negative pressure via a negative pressure pipe (8) . The negative pressure chamber (51b) is so constituted as to be supplied with a negative pressure to have a target pressure that is set relative to the atmospheric pressure.