A straddled vehicle comprising: an engine unit including: a crankshaft ; a crankshaft supporter supporting the crankshaft ; a gearbox having gear positions with which a rotation speed of the crankshaft is changed at different transmission ratios, respectively, and power input from the crankshaft is transmitted to a driving wheel and a gear position in which the power input from the crankshaft is not transmitted to the driving wheel ; and a gearbox supporter supporting the gearbox , the crankshaft supporter and the gearbox supporter being integrally molded; a contactless engine rotation speed sensor configured to detect an engine rotation speed; a contactless vehicle speed sensor configured to detect a vehicle speed; a gear position sensor provided in the gearbox supporter to detect the gear position of the gearbox ; and a gear position sensor failure detector configured to detect a failure of the gear position sensor , the gear position sensor failure detector including: a gear position estimation unit configured to estimate the gear position of the gearbox based on a signal from the engine rotation speed sensor and a signal from the vehicle speed sensor ; and a failure determination unit configured to determine whether there is a failure of the gear position sensor by comparing the gear position estimated by the gear position estimation unit with the gear position detected by the gear position sensor . an engine unit including: a crankshaft ; a crankshaft supporter supporting the crankshaft ; a gearbox having gear positions with which a rotation speed of the crankshaft is changed at different transmission ratios, respectively, and power input from the crankshaft is transmitted to a driving wheel and a gear position in which the power input from the crankshaft is not transmitted to the driving wheel ; and a gearbox supporter supporting the gearbox , the crankshaft supporter and the gearbox supporter being integrally molded; a contactless engine rotation speed sensor configured to detect an engine rotation speed; a contactless vehicle speed sensor configured to detect a vehicle speed; a gear position sensor provided in the gearbox supporter to detect the gear position of the gearbox ; and a gear position sensor failure detector configured to detect a failure of the gear position sensor , the gear position sensor failure detector including: a gear position estimation unit configured to estimate the gear position of the gearbox based on a signal from the engine rotation speed sensor and a signal from the vehicle speed sensor ; and a failure determination unit configured to determine whether there is a failure of the gear position sensor by comparing the gear position estimated by the gear position estimation unit with the gear position detected by the gear position sensor . a gear position estimation unit configured to estimate the gear position of the gearbox based on a signal from the engine rotation speed sensor and a signal from the vehicle speed sensor ; and a failure determination unit configured to determine whether there is a failure of the gear position sensor by comparing the gear position estimated by the gear position estimation unit with the gear position detected by the gear position sensor . <EOS>