A wheel loader comprising: an engine; a travel device driven by the engine; a transmission that transmits driving power from the engine to the travel device; and a vehicle body frame that supports the transmission, wherein the transmission has: an input shaft extending in a vehicle front-back direction; an output shaft extending in the vehicle front-back direction; a gear mechanism that transmits rotation of the input shaft to the output shaft, the gear mechanism including a middle shaft arranged under the input shaft and extending in the vehicle front-back direction and a planetary gear mechanism (68, 69) connected to the middle shaft; a transmission case that houses the input shaft, the gear mechanism, and the output shaft; a first motor connected to a first rotating element of the planetary gear mechanism (68, 69), the first motor being attached to the transmission case; a second motor connected to a second rotating element of the planetary gear mechanism (68, 69), the second motor being attached to the transmission case; and, the transmission is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speeds of the first motor and the second motor; the transmission case has an input shaft case for housing the input shaft; and the first motor and the second motor are arranged below the input shaft; characterized in that a lower part of the input shaft case includes a curved surface part that is curved so as to protrude downward and at least a portion of the first motor and the second motor overlaps the curved surface part as seen in a projection view in the up-down direction. an engine; a travel device driven by the engine; a transmission that transmits driving power from the engine to the travel device; and a vehicle body frame that supports the transmission, wherein the transmission has: an input shaft extending in a vehicle front-back direction; an output shaft extending in the vehicle front-back direction; a gear mechanism that transmits rotation of the input shaft to the output shaft, the gear mechanism including a middle shaft arranged under the input shaft and extending in the vehicle front-back direction and a planetary gear mechanism (68, 69) connected to the middle shaft; a transmission case that houses the input shaft, the gear mechanism, and the output shaft; a first motor connected to a first rotating element of the planetary gear mechanism (68, 69), the first motor being attached to the transmission case; a second motor connected to a second rotating element of the planetary gear mechanism (68, 69), the second motor being attached to the transmission case; and, the transmission is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speeds of the first motor and the second motor; the transmission case has an input shaft case for housing the input shaft; and the first motor and the second motor are arranged below the input shaft; characterized in that a lower part of the input shaft case includes a curved surface part that is curved so as to protrude downward and at least a portion of the first motor and the second motor overlaps the curved surface part as seen in a projection view in the up-down direction. an input shaft extending in a vehicle front-back direction; an output shaft extending in the vehicle front-back direction; a gear mechanism that transmits rotation of the input shaft to the output shaft, the gear mechanism including a middle shaft arranged under the input shaft and extending in the vehicle front-back direction and a planetary gear mechanism (68, 69) connected to the middle shaft; a transmission case that houses the input shaft, the gear mechanism, and the output shaft; a first motor connected to a first rotating element of the planetary gear mechanism (68, 69), the first motor being attached to the transmission case; a second motor connected to a second rotating element of the planetary gear mechanism (68, 69), the second motor being attached to the transmission case; and, the transmission is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speeds of the first motor and the second motor; the transmission case has an input shaft case for housing the input shaft; and the first motor and the second motor are arranged below the input shaft; characterized in that a lower part of the input shaft case includes a curved surface part that is curved so as to protrude downward and at least a portion of the first motor and the second motor overlaps the curved surface part as seen in a projection view in the up-down direction.