A saddle-type vehicle comprising: a vehicle body frame including a main frame, the main frame passing through a center of the saddle-type vehicle; a seat on which a driver is seated; a fuel tank disposed in front of the seat; an engine disposed below the fuel tank and including a crankcase and a cylinder protruding upward from a front portion of the crankcase; and a fuel vapor passage connected to the fuel tank and configured to discharge evaporated fuel in the fuel tank to an outside of the fuel tank, wherein at least a part of the fuel vapor passage passes behind the cylinder, characterized in that a) the saddle-type vehicle further comprises: an intake device extending rearward from the cylinder and including an inlet pipe, a throttle body, a connecting tube, and an air cleaner box; and an air introduction passage connecting part provided in a middle of the fuel vapor passage and connected to an air introduction passage for introducing air into the fuel vapor passage, wherein the air introduction passage connecting part is placed below the fuel tank and also in front of the air cleaner box, a seat frame that supports the seat and is arranged to extend rearward and upward; and a second check valve provided in a middle of the air introduction passage and configured to stop a flow from the engine side toward the atmospheric side, wherein at least a part of the air introduction passage located downstream of the second check valve is arranged forward and downward along the seat frame b) the fuel vapor passage crosses the main frame in a plan view, and then extends downward along a rear portion of the main frame below the fuel tank while being interposed between the rear portion of the main frame and a connecting tube of an intake device, c) the fuel vapor passage is connected to the crankcase at a portion in a rear side of the cylinder and opens toward oil in the engine, and d) the fuel vapor passage is inclined downward toward the air introduction passage connecting part disposed at a downstream side of the fuel vapor passage. a vehicle body frame including a main frame, the main frame passing through a center of the saddle-type vehicle; a seat on which a driver is seated; a fuel tank disposed in front of the seat; an engine disposed below the fuel tank and including a crankcase and a cylinder protruding upward from a front portion of the crankcase; and a fuel vapor passage connected to the fuel tank and configured to discharge evaporated fuel in the fuel tank to an outside of the fuel tank, wherein at least a part of the fuel vapor passage passes behind the cylinder, a) the saddle-type vehicle further comprises: an intake device extending rearward from the cylinder and including an inlet pipe, a throttle body, a connecting tube, and an air cleaner box; and an air introduction passage connecting part provided in a middle of the fuel vapor passage and connected to an air introduction passage for introducing air into the fuel vapor passage, wherein the air introduction passage connecting part is placed below the fuel tank and also in front of the air cleaner box, a seat frame that supports the seat and is arranged to extend rearward and upward; and a second check valve provided in a middle of the air introduction passage and configured to stop a flow from the engine side toward the atmospheric side, wherein at least a part of the air introduction passage located downstream of the second check valve is arranged forward and downward along the seat frame an intake device extending rearward from the cylinder and including an inlet pipe, a throttle body, a connecting tube, and an air cleaner box; and an air introduction passage connecting part provided in a middle of the fuel vapor passage and connected to an air introduction passage for introducing air into the fuel vapor passage, wherein the air introduction passage connecting part is placed below the fuel tank and also in front of the air cleaner box, a seat frame that supports the seat and is arranged to extend rearward and upward; and a second check valve provided in a middle of the air introduction passage and configured to stop a flow from the engine side toward the atmospheric side, wherein at least a part of the air introduction passage located downstream of the second check valve is arranged forward and downward along the seat frame b) the fuel vapor passage crosses the main frame in a plan view, and then extends downward along a rear portion of the main frame below the fuel tank while being interposed between the rear portion of the main frame and a connecting tube of an intake device, c) the fuel vapor passage is connected to the crankcase at a portion in a rear side of the cylinder and opens toward oil in the engine, and d) the fuel vapor passage is inclined downward toward the air introduction passage connecting part disposed at a downstream side of the fuel vapor passage.