A traveling direction velocity calculation device 1 calculates a posture of an acceleration sensor 10 with respect to a user, using a detection result represented in a local coordinate system associated with the acceleration sensor 10, detecting acceleration, which is worn on a users body, when a change in the detection result of the acceleration sensor 10 satisfies a predetermined specific condition. The detection result of the acceleration sensor 10 at a time different from that when the posture is calculated and at a time when the specific condition is satisfied is transformed, using the calculated posture, to a mobile body coordinate system associated with a user. A velocity in a traveling direction of the user is calculated using the transformed detection result.
