BLOWBY GAS TREATMENT DEVICE

A blowby gas treatment device is configured to discharge blowby gas inside an internal combustion engine (10) to an intake passage (13) inside an intake manifold (12). The blowby gas treatment device includes a blowby gas passage (15), a flow control valve (18), a communication hole (40), and a lid (50). The blowby gas passage (15) includes an engine gas passage (16) and an intake manifold gas passage (17). The communication hole (40) is provided in the intake manifold (12). The communication hole (40) is configured to connect outside of the intake manifold (12) and a part of the intake manifold gas passage (17) on a downstream side of the flow control valve (18) in a gas flow direction. The communication hole (40) opens the intake manifold gas passage (17) to the atmosphere. A lid (50) is configured to open and close the communication hole (40).