An intermediate image transfer type "of colour image" forming apparatus comprising: an image carrier (40Y, 40M, 40C, 40K); an intermediate image transfer body to which a single-color toner image formed with a spherical toner having a mean circularity of 0.95 or above is arranged to be transferred from said image carrier (40Y, 40M, 40C, 40K), wherein, assuming that the maximum amount of toner to deposit on the line portion of the toner image and a maximum amount of toner to deposit on a solid portion of said toner image are a mg/cm 2 and b mg/cm 2, respectively, a ratio a/b lies in a range of 1.0 ≤ a/b ≤ 1.6; primary image transferring means (62Y, 62M, 62C, 62K) for transferring the toner image from said image carrier (40Y, 40M, 40C, 40K) to said intermediate image transfer body; and secondary image transferring means for transferring the toner image from said intermediate image transfer body to a recording medium; wherein said primary image transferring means (62Y, 62M, 62C, 62K) comprises primary bias applying means for applying a primary image transfer bias to said intermediate image transfer body, wherein a surface of said intermediate image transfer body to which the primary or the secondary image transfer bias is applied has a surface resistivity ranging from 10 7 Ω/□ to 10 12 Ω/□, and wherein said intermediate image transfer body is configured to have a surface potential attenuation ratio that attenuates, before a portion of said intermediate image transfer body applied with the primary image transfer bias V 0 is subject to a next primary image transfer, a potential remaining on said portion to V 0 /2 or below in T seconds, assuming that a period of time between preceding primary image transfer and following image transfer is T seconds. an image carrier (40Y, 40M, 40C, 40K); an intermediate image transfer body to which a single-color toner image formed with a spherical toner having a mean circularity of 0.95 or above is arranged to be transferred from said image carrier (40Y, 40M, 40C, 40K), wherein, assuming that the maximum amount of toner to deposit on the line portion of the toner image and a maximum amount of toner to deposit on a solid portion of said toner image are a mg/cm 2 and b mg/cm 2, respectively, a ratio a/b lies in a range of 1.0 ≤ a/b ≤ 1.6; primary image transferring means (62Y, 62M, 62C, 62K) for transferring the toner image from said image carrier (40Y, 40M, 40C, 40K) to said intermediate image transfer body; and secondary image transferring means for transferring the toner image from said intermediate image transfer body to a recording medium; wherein said primary image transferring means (62Y, 62M, 62C, 62K) comprises primary bias applying means for applying a primary image transfer bias to said intermediate image transfer body, wherein a surface of said intermediate image transfer body to which the primary or the secondary image transfer bias is applied has a surface resistivity ranging from 10 7 Ω/□ to 10 12 Ω/□, and wherein said intermediate image transfer body is configured to have a surface potential attenuation ratio that attenuates, before a portion of said intermediate image transfer body applied with the primary image transfer bias V 0 is subject to a next primary image transfer, a potential remaining on said portion to V 0 /2 or below in T seconds, assuming that a period of time between preceding primary image transfer and following image transfer is T seconds.