An instrument device of a motorcycle is provided which is provided with air vents into which water cannot penetrate, without the number of parts being increased and influence on the appearance of the instrument device. The instrument device of the motor cycle has instrument equipment (60), and an upper housing (51) and a lower housing (53) which accommodate the instrument equipment (60). The lower housing (53) is provided with a connecting hole (70) into which a connecting part (56) which connects the lower housing (53) to the instrument equipment (60) is inserted. An air vent (72) which communicates the internal space (50b) of the instrument equipment (60) with the outside is disposed in a boss (71) which forms the connecting hole (70). The boss (71) is disposed in a position n the lower housing (53) near the upper part of the vehicle body. The boss (71) is composed of a cylindrical part having a round bottom, the cylindrical part is vertically arranged from the bottom of the lower housing (53) to the upper side of the vehicle body. The air vent (72) is disposed in the inner side face, near the front side of the vehicle body, of the upper part of the bottom (73) of the boss (71).