A construction machine comprising: a vehicle body (2, 3); a vehicle body frame including a center frame disposed in the center in the right-and-left direction of the vehicle body (2, 3), a left side frame provided on the left side of the center frame and extending in a front-and-rear direction of the vehicle body (2, 3), and a right side frame provided on the right side of the center frame and extending in the front-and-rear direction of the vehicle body (2, 3); a tank attachment site (9B, 10B) located and provided on one side in the right-and-left direction of the vehicle body frame; and an oil reservoir tank storing oil liquids provided at the tank attachment site (9B, 10B), wherein the tank attachment site (9B, 10B) is provided with a pair of tank support bases (18, 19) supporting the oil reservoir tank at a position at which a bottom surface portion of the oil reservoir tank is separated upward from the tank attachment site (9B, 10B), the pair of tank support bases (18, 19) is disposed separately in the front-and-rear direction of the vehicle body (2, 3), the oil reservoir tank is supported by the tank support base (18, 19) at a position higher than that of an upper surface of either the left side frame or the right side frame, a space portion with an opening corresponding to an outer side in the right-and-left direction of the vehicle body (2, 3) opposite to the center frame is provided between the tank attachment site (9B, 10B) and the bottom surface portion of the oil reservoir tank, characterized in that: the space portion accommodates a tool receiver, the opening of the space portion is provided with an opening/closing cover openably closing the opening, the bottom surface portion of the hydraulic oil tank is provided with a supply pipe supplying oil liquid and a discharge pipe discharging oil liquid, the hydraulic oil tank is supported on the tank support base (18, 19) such that the supply pipe and the discharge pipe are accommodated in the space portion, and the tank support base (18, 19) is set in a dimension so as to allow connecting work to the supply pipe, drainage work performed through the discharge pipe, and the tool receiver and tools to be taken in and out of the space mounted on the tool receiver. a vehicle body (2, 3); a vehicle body frame including a center frame disposed in the center in the right-and-left direction of the vehicle body (2, 3), a left side frame provided on the left side of the center frame and extending in a front-and-rear direction of the vehicle body (2, 3), and a right side frame provided on the right side of the center frame and extending in the front-and-rear direction of the vehicle body (2, 3); a tank attachment site (9B, 10B) located and provided on one side in the right-and-left direction of the vehicle body frame; and an oil reservoir tank storing oil liquids provided at the tank attachment site (9B, 10B), wherein the tank attachment site (9B, 10B) is provided with a pair of tank support bases (18, 19) supporting the oil reservoir tank at a position at which a bottom surface portion of the oil reservoir tank is separated upward from the tank attachment site (9B, 10B), the pair of tank support bases (18, 19) is disposed separately in the front-and-rear direction of the vehicle body (2, 3), the oil reservoir tank is supported by the tank support base (18, 19) at a position higher than that of an upper surface of either the left side frame or the right side frame, a space portion with an opening corresponding to an outer side in the right-and-left direction of the vehicle body (2, 3) opposite to the center frame is provided between the tank attachment site (9B, 10B) and the bottom surface portion of the oil reservoir tank, the space portion accommodates a tool receiver, the opening of the space portion is provided with an opening/closing cover openably closing the opening, the bottom surface portion of the hydraulic oil tank is provided with a supply pipe supplying oil liquid and a discharge pipe discharging oil liquid, the hydraulic oil tank is supported on the tank support base (18, 19) such that the supply pipe and the discharge pipe are accommodated in the space portion, and the tank support base (18, 19) is set in a dimension so as to allow connecting work to the supply pipe, drainage work performed through the discharge pipe, and the tool receiver and tools to be taken in and out of the space mounted on the tool receiver.