A component-mounting apparatus and a component-positioning unit for positioning a component, having a simple structure with reduced manufacturing cost and a significantly higher component-mounting speed. The component-mounting apparatus includes a holding device that holds a component and moves horizontally and a positioning device having a sloped portion for positioning the component held by the holding device when the component comes into contact with the sloped portion. The positioning device comprises a first rotatable roller member having a sloped side surface with which the component comes into contact; and the horizontal movement speed of the holding device substantially agrees with the horizontal component of the peripheral velocity of the first roller member, with which the component comes into contact.