An outboard motor has an internal combustion engine with a carburetor. The carburetor is designed to extend maintenance interval greatly by preventing or suppressing the deposition of solid matters in the gap between the intake passage and a butterfly-type throttle valve therein. The throttle valve is divided, by a valve axis about which the throttle valve turns, into a first valve part that turns from the downstream side to the upstream side with respect to an air intake direction when the fully closed throttle valve is opened and a second valve part that turns from the upstream side to the downstream side with respect to the air intake direction when the fully closed throttle valve is opened. The first valve part has an edge that moves to the upstream side past bypass ports when the fully closed throttle valve is opened, and the second valve part is provided with a through hole that allows air to flow therethrough at a flow rate necessary for idling when the throttle valve is fully closed.