A risk index transformation apparatus includes a state acquisition portion, an index calculation portion, an index transformation portion, and a support method determination portion. The state acquisition portion acquires a vehicle state. The index calculation portion calculates the risk index based on the vehicle state acquired by the state acquisition portion. The index transformation portion performs a correction operation to transform the risk index calculated by the index calculation portion using a threshold value and a value of a continuous function that continuously changes with reference to the threshold value. The support method determination portion controls a device to execute a support method based on the risk index transformed by the index transformation portion using the correction operation. The support method includes a display of warning in multiple levels, an output of alarm sound in multiple levels, or an operation restriction of a navigation device.