Step platform device for connection to a trailer hitch ball, the step platform device comprising: - a trailer hitch ball connection device comprising first and second connection elements (30, 40) pivotably connected to each other by means of a first connection device about a first axis; where the trailer hitch ball connection device comprises a ball connection interface comprising a first subinterface provided on the first connection element and a second subinterface provided on the second connection element; - a platform device provided above the trailer hitch ball connection device; where the platform device comprises an upwardly facing step surface and a platform element provided below the step surface; - a link device comprising a link element; - the step platform device is configured to be provided in a closed state and in an open state, where the ball connection interface may be connected onto the trailer hitch ball in the closed state and where the ball connection interface may be moved away from the trailer hitch ball in the open state; characterized in that: - the platform element and the first connection element are pivotably connected to each other about a second axis by means of a second connection device; - the link element and the second connection element are pivotably connected to each other about a third axis by means of a third connection device; - the platform element and the link element are pivotably connected to each other about a fourth axis by means of a fourth connection device; - the step platform device is configured to be brought from the closed state to the open state by moving the first and fourth connection devices (15, 18) away from each other, thereby causing the second and third connection devices (16, 17) to move towards each other; - the step platform device is configured to be brought from the open state to the closed state by moving the first and fourth connection devices (15, 18) towards each other, thereby causing the second and third connection devices (16, 17) to move away from each other; - the connection interface is provided below the first connection device and where the second and third connection devices (16, 17) are provided above the first connection device. - a trailer hitch ball connection device comprising first and second connection elements (30, 40) pivotably connected to each other by means of a first connection device about a first axis; where the trailer hitch ball connection device comprises a ball connection interface comprising a first subinterface provided on the first connection element and a second subinterface provided on the second connection element; - a platform device provided above the trailer hitch ball connection device; where the platform device comprises an upwardly facing step surface and a platform element provided below the step surface; - a link device comprising a link element; - the step platform device is configured to be provided in a closed state and in an open state, where the ball connection interface may be connected onto the trailer hitch ball in the closed state and where the ball connection interface may be moved away from the trailer hitch ball in the open state; - the platform element and the first connection element are pivotably connected to each other about a second axis by means of a second connection device; - the link element and the second connection element are pivotably connected to each other about a third axis by means of a third connection device; - the platform element and the link element are pivotably connected to each other about a fourth axis by means of a fourth connection device; - the step platform device is configured to be brought from the closed state to the open state by moving the first and fourth connection devices (15, 18) away from each other, thereby causing the second and third connection devices (16, 17) to move towards each other; - the step platform device is configured to be brought from the open state to the closed state by moving the first and fourth connection devices (15, 18) towards each other, thereby causing the second and third connection devices (16, 17) to move away from each other; - the connection interface is provided below the first connection device and where the second and third connection devices (16, 17) are provided above the first connection device.