To provide a platen which prevents a recording medium (a recording medium) from floating up while avoiding dart of a back surface of recording paper (a recording medium) due to ink mists, and also to provide a recorder and a liquid injection apparatus each provided with the platen.

Upstream ribs 633a to n and downstream ribs 634a to n are arranged at a predetermined interval on a surface which supports recording paper 300, and characteristically a rib width of the downstream ribs, 634a, 634h, 634j, 634k, 634m, and 634n which support the side end of the recording paper 300 is formed greater than that of the other downstream ribs. A space between the downstream ribs, 634a, 634h, 634j, 634k, 634m, and 634n, and the back surface of the recording paper 300 is thereby eliminated, so that the floating-up of the recording paper 300 is prevented while the dirt of back surface of the recording paper 300 due to ink mists or the like is avoided.