AbstractRed supergiants (RSGs) are progenitors of Type IIP supernovae (SNe). It is suggested that RSGs can experience a mass loss with a very high mass-loss rate (even as high as 0.01 M_⊙ yr⁻¹) due to, e.g., dynamical instabilities of their envelopes (e.g., Yoon & Cantiello (2010)). Because of the extensive mass loss, RSGs can have very dense circumstellar medium (CSM) around them. If a SN explosion occurs soon after the extensive mass loss of a RSG, the SN ejecta will collide with the dense CSM. Due to the collision, the kinetic energy of the ejecta is converted to radiation energy and such SNe with collision can be brighter than usual Type IIP SNe. By performing one-dimensional multi-group radiation hydrodynamical calculations, we investigate the effects of the collision on Type IIP SN LCs. We show that if RSGs explode within a dense CSM, the SN will be very bright, especially in ultraviolet, at early epochs. We also compare our models with the ultraviolet-bright Type IIP SN 2009kf and show that the progenitor of SN 2009kf can be a massive RSG which experienced extensive mass loss just before its explosion. We conclude that this is evidence that massive RSGs experience extensive mass loss and the existence of such mass loss can actually be the cause of the contradiction between theoretical and observational mass ranges of Type IIP SN progenitors.