An outboard engine unit comprising an outboard engine unit body and mounting means configured to be detachable from a hull, the mounting means being provided on a front side of the outboard engine unit body, and the outboard engine unit body having an engine, an engine cover for covering the engine, and a throttle unit in communication with an upper space in a rear-side interior of the engine cover, wherein the outboard engine unit comprises: a cooling opening, disposed in an upper part of the engine cover, for guiding air to an interior of the engine cover; an air guide disposed along a reverse surface side of a top part of the engine cover to form a first intake channel communicating with the opening and extending to an upper front end of the engine cover along an upper-side interior of the engine cover, the air guide being provided with a guide bottom part disposed along the top part of the engine cover, a first outlet disposed at a front end of the guide bottom part, and a sidewall disposed behind the first outlet, the first outlet forming an outlet of the first intake channel and facing a front-side space in the engine cover, the upper space being defined below the air guide bottom part of the air guide, above the engine and in a space disposed above a rear interior of the engine cover; a partition wall, disposed to be oriented substantially vertically below the first outlet, for guiding air directed out from the first outlet to below the engine cover; and a second intake channel, extending substantially vertically along a rear wall of the engine cover rearwardly of the partition wall, for communicating a second outlet at an upper end of the engine unit with the upper space, wherein the second intake channel has a second inlet at a lower end part thereof such that the second inlet communicates with a lower-side interior of the engine cover defined adjacent to the rear wall of the engine cover, the lower-side interior of the engine cover being in communication with the front-side space in the engine cover. a cooling opening, disposed in an upper part of the engine cover, for guiding air to an interior of the engine cover; an air guide disposed along a reverse surface side of a top part of the engine cover to form a first intake channel communicating with the opening and extending to an upper front end of the engine cover along an upper-side interior of the engine cover, the air guide being provided with a guide bottom part disposed along the top part of the engine cover, a first outlet disposed at a front end of the guide bottom part, and a sidewall disposed behind the first outlet, the first outlet forming an outlet of the first intake channel and facing a front-side space in the engine cover, the upper space being defined below the air guide bottom part of the air guide, above the engine and in a space disposed above a rear interior of the engine cover; a partition wall, disposed to be oriented substantially vertically below the first outlet, for guiding air directed out from the first outlet to below the engine cover; and a second intake channel, extending substantially vertically along a rear wall of the engine cover rearwardly of the partition wall, for communicating a second outlet at an upper end of the engine unit with the upper space, wherein the second intake channel has a second inlet at a lower end part thereof such that the second inlet communicates with a lower-side interior of the engine cover defined adjacent to the rear wall of the engine cover, the lower-side interior of the engine cover being in communication with the front-side space in the engine cover.