A main frame (11) is configured to attach a boom (13) to a working vehicle and comprises a first frame (110) and a second frame (120). The first frame (110) is to be fixed to the vehicle body (1) and includes: a first support part (111) having a first support surface (111a) arranged on the first virtual plane (P1) and a second support part (112) having a second support surface (112a) arranged on a second virtual plane (P2). The second frame (120) is to support the boom (13), and includes: a first attachment (121) to be fixed to the first support part (111) and has a first attachment surface (121a) to abut the first support surface (111a) and a second attachment (123) to be fixed to the second support part (112) and has a second attachment surface (123a) to abut the second support surface (112a). The second frame (120) further includes a mast (122) extending in an up-down direction, in use.
