1. An image processing apparatus comprising: an image-conversion-parameter storage unit having stored therein in advance, as image conversion parameters to coordinate-convert images of in-vehicle cameras incorporated in an own vehicle, a plurality of directions connecting between a sight-line starting position of a driver and a plurality of predetermined positions of the own vehicle, values of a depression angle from the sight-line starting position of the driver, and a range that the driver is caused to visualize corresponding to a positioned state of the own vehicle, for each of the in-vehicle cameras incorporated at different positions of the own vehicle; a state determining unit that determines a current state of the own vehicle; an image converting unit that coordinate-converts an image captured by each in-vehicle camera, based on a result of a state determined by the state determining unit and the image conversion parameters stored in the image-conversion-parameter storage unit; a display and output unit that outputs and displays an image converted by the image converting unit; a display-output-condition-input receiving unit that receives from a driver an input of a display output condition for outputting and displaying an image captured by each in-vehicle camera; and an overhead-image display unit that temporarily displays an overhead image of entirety of the own vehicle when the display-output-condition-input receiving unit receives an input of a first display output condition different from a second display output condition of last time, wherein the overhead image is inserted between a first image converted in the first display output condition and a second image converted in the second display output condition, before the first image is displayed, and the first image and the second image are respectively one and another out of an image acquired from the driver's viewpoint viewing frontward of the own vehicle from a driver position, an image acquired from the driver's viewpoint viewing backward of the own vehicle from the driver position, and an image acquired from the driver's viewpoint viewing sideward of the own vehicle from the driver position.