An image forming apparatus comprising: a carriage vertically movable between an upper position and a lower position and including an image forming unit that ejects liquid onto a recording medium to form an image on the recording medium, wherein the carriage comprises a height adjustment mechanism to change a height of the carriage between the upper position and the lower position, the height adjustment mechanism including a cam member and a first and second rotation guide member (503, 504); a guide member to support the height adjustment mechanism and to guide the carriage in a main scanning direction; and a pressing member to drive the cam member, the rotation guide member being pressed against the pressing member to be rotated during movement of the carriage in the main scanning direction to drive the cam member and change the height of the carriage, wherein upon a change in the height of the carriage from the upper position to the lower position, the carriage moves through at least a part of a range extending from one end to an opposite end of the guide member at a speed slower than a speed of the carriage during image formation to contact a rotation guide member (503, 504) and the pressing member against each other at the slower speed, wherein the first rotation guide member is configured to drive the cam member to rotate in a direction to lift the carriage and wherein the second rotation guide member is configured to drive the cam member to rotate in a direction to lower the carriage, wherein each of the rotation guide members (503, 504) has a contact surface (513, 514) wherein at least a portion of the contact surface (513, 514) is sloped, and wherein the sloped portion of the contact surface of the first rotation guide member is more gently sloped than the sloped portion of the contact part of the second rotation guide member. a carriage vertically movable between an upper position and a lower position and including an image forming unit that ejects liquid onto a recording medium to form an image on the recording medium, wherein the carriage comprises a height adjustment mechanism to change a height of the carriage between the upper position and the lower position, the height adjustment mechanism including a cam member and a first and second rotation guide member (503, 504); a guide member to support the height adjustment mechanism and to guide the carriage in a main scanning direction; and a pressing member to drive the cam member, the rotation guide member being pressed against the pressing member to be rotated during movement of the carriage in the main scanning direction to drive the cam member and change the height of the carriage, wherein upon a change in the height of the carriage from the upper position to the lower position, the carriage moves through at least a part of a range extending from one end to an opposite end of the guide member at a speed slower than a speed of the carriage during image formation to contact a rotation guide member (503, 504) and the pressing member against each other at the slower speed, wherein the first rotation guide member is configured to drive the cam member to rotate in a direction to lift the carriage and wherein the second rotation guide member is configured to drive the cam member to rotate in a direction to lower the carriage, wherein each of the rotation guide members (503, 504) has a contact surface (513, 514) wherein at least a portion of the contact surface (513, 514) is sloped, and wherein the sloped portion of the contact surface of the first rotation guide member is more gently sloped than the sloped portion of the contact part of the second rotation guide member.