An air intake device for an engine is provided that includes a throttle body (1), a throttle valve (5) that has a valve shaft (5a) rotatably supported on the throttle body (1), a throttle drum (8) connected to one end of the throttle valve (5), a throttle sensor (51) connected to the other end of the valve shaft (5a), a bypass (20) bypassing the throttle valve (5), and a bypass valve (25) that opens and closes the bypass (20), a bearing boss (3) supporting one end part, on the throttle drum (8) side, of the valve shaft (5a) being integrally and projecting provided on one side face of the throttle body (1), wherein the bypass (20) is formed so as to surround the bearing boss (3). This enables the air intake device for an engine to be made compact in spite of the bypass being present.