A component mounter comprising: a component supply means configured to supply a component; a component pickup means configured to pick up the component; a moving means (26, 30, 45) configured to move the component pickup means; a board holding means (20, 23) configured to hold a board on which the component is to be mounted; a temporary placement surface having a hole at a specified position; a pressure adjustment means (76, 77, 78) configured to supply at least negative pressure to the hole; a pressure detecting device configured to detect pressure at the hole; and a control means configured to control the component pickup means and the moving means (26, 30, 45) such that after the component supplied by the component supply means has been picked up by the component pickup means and before the component is mounted on the board, the component is temporarily placed at the specified position, wherein the control means being further configured to, after performing control to temporarily place the component at the specified position, determine whether the component has actually been temporarily placed at the specified position based on the pressure state of the hole with negative pressure being supplied to the hole, and perform processing based on the determination result. characterized by a sideways imaging means configured to image the component picked up by the component pickup means from the side, wherein the control means is further configured to, if the determination result is negative, image the component pickup means using the sideways imaging means, determine whether the component pickup means is holding the component based on the image, report the determination result to an operator, and stop processing. a component supply means configured to supply a component; a component pickup means configured to pick up the component; a moving means (26, 30, 45) configured to move the component pickup means; a board holding means (20, 23) configured to hold a board on which the component is to be mounted; a temporary placement surface having a hole at a specified position; a pressure adjustment means (76, 77, 78) configured to supply at least negative pressure to the hole; a pressure detecting device configured to detect pressure at the hole; and a control means configured to control the component pickup means and the moving means (26, 30, 45) such that after the component supplied by the component supply means has been picked up by the component pickup means and before the component is mounted on the board, the component is temporarily placed at the specified position, wherein the control means being further configured to, after performing control to temporarily place the component at the specified position, determine whether the component has actually been temporarily placed at the specified position based on the pressure state of the hole with negative pressure being supplied to the hole, and perform processing based on the determination result. characterized by a sideways imaging means configured to image the component picked up by the component pickup means from the side, wherein the control means is further configured to, if the determination result is negative, image the component pickup means using the sideways imaging means, determine whether the component pickup means is holding the component based on the image, report the determination result to an operator, and stop processing.