A method, used in a portable navigation device comprising an acceleration sensor, of determining a driving state, the method comprising: reading sensor output signals of different axes from the acceleration sensor while a vehicle is being driven wherein the acceleration sensor is an at least two axes acceleration sensor and detects an acceleration of the vehicle; and comparing the read sensor output signals of the different axes and determining whether the vehicle is in a turning state, wherein one axis of the at least two axes of the acceleration sensor outputs an acceleration sensor signal Y with respect to a driving direction of the vehicle, and another axis of the acceleration sensor outputs an acceleration signal X with respect to a left/right direction of the vehicle, wherein the comparing and the determining comprise: calculating an absolute value |Y| of the acceleration sensor signal Y with respect to the driving direction and an absolute value |X| of the acceleration sensor signal X with respect to the left/right direction; determining that the vehicle is in the straight-driving state when the absolute value |Y| is greater than the absolute value |X|; determining that the vehicle is in the turning state when the absolute value |X| is greater than the absolute value |Y|; and determining whether the vehicle is in a right-turning state or in a left-turning state depending on whether the level difference value X-Y is a positive number or a negative number wherein the method further comprises using information determined in the determining steps about the straight-driving state or the turning state of the vehicle when the portable navigation device calculates the current location of the vehicle or when the portable navigation device guides a user along a path to a destination designated by a user. reading sensor output signals of different axes from the acceleration sensor while a vehicle is being driven wherein the acceleration sensor is an at least two axes acceleration sensor and detects an acceleration of the vehicle; and comparing the read sensor output signals of the different axes and determining whether the vehicle is in a turning state, wherein one axis of the at least two axes of the acceleration sensor outputs an acceleration sensor signal Y with respect to a driving direction of the vehicle, and another axis of the acceleration sensor outputs an acceleration signal X with respect to a left/right direction of the vehicle, wherein the comparing and the determining comprise: calculating an absolute value |Y| of the acceleration sensor signal Y with respect to the driving direction and an absolute value |X| of the acceleration sensor signal X with respect to the left/right direction; determining that the vehicle is in the straight-driving state when the absolute value |Y| is greater than the absolute value |X|; determining that the vehicle is in the turning state when the absolute value |X| is greater than the absolute value |Y|; and determining whether the vehicle is in a right-turning state or in a left-turning state depending on whether the level difference value X-Y is a positive number or a negative number wherein the method further comprises using information determined in the determining steps about the straight-driving state or the turning state of the vehicle when the portable navigation device calculates the current location of the vehicle or when the portable navigation device guides a user along a path to a destination designated by a user. calculating an absolute value |Y| of the acceleration sensor signal Y with respect to the driving direction and an absolute value |X| of the acceleration sensor signal X with respect to the left/right direction; determining that the vehicle is in the straight-driving state when the absolute value |Y| is greater than the absolute value |X|; determining that the vehicle is in the turning state when the absolute value |X| is greater than the absolute value |Y|; and determining whether the vehicle is in a right-turning state or in a left-turning state depending on whether the level difference value X-Y is a positive number or a negative number wherein the method further comprises using information determined in the determining steps about the straight-driving state or the turning state of the vehicle when the portable navigation device calculates the current location of the vehicle or when the portable navigation device guides a user along a path to a destination designated by a user.