A modular cross flow fan comprises a housing, a cross flow fan and a motor. The housing has an upper wall, a lower wall and two side boards. The housing is formed with an accommodating space, an inflow opening and an outflow opening. The direction of inflow and the direction of outflow lie in a line. The cross flow fan is disposed in the accommodating space. The motor is disposed at the housing and connected to the cross flow fan. Furthermore, an air conditioning device is provided, comprising modular cross flow fan, a flow channel and a heat exchanger. The flow channel is joined to the inflow opening. The heat exchanger is disposed in the flow channel proximal to the inflow opening. Ambient air can flow horizontally through the flow channel, the inflow opening, and into the housing.