An imaging device determines whether, in an image captured by an imaging unit, straight lines exist which meet a condition of automatic vertical line determination (S14). If straight lines meeting the condition exist (YES in S15), the imaging device performs a vertical line determination process to extract vertical lines and so on (S16). On LCD, the imaging device displays the vertical lines extracted in S16 together with auxiliary lines including one connecting a calculated vanishing point and a target point (S17). The imaging device detects its inclination based on these lines including the vertical lines, and displays a message of “OK” on LCD when the inclination is within a predetermined range to notify a user to that effect. Thus, without increasing the manufacturing cost, the imaging device can prevent a user from capturing a target object while the imaging device is inclined to the horizontal direction in an image space.