To provide a plate type heat exchanger that does not require the provision of any disturbance element for promoting heat exchange.

A plate type heat exchanger is provided with first plates 10 and second plates 12, which are laminated alternately. The first plate 10 is provided with a bottom surface 14 having corrugated parts 18. The second plate 12 is provided with a bottom surface 20 having the corrugated parts 24. The corrugated parts 18, 24 are substantially orthogonal to each other and first flow passages 34 for first fluid (F1) and second flow passages 36 for second fluid (F2) are formed alternately. The flow passages 34, 36 are provided with the hydraulic diameter (Dh) of 1-3 mm obtained by Dh=2×h employing (h) showing the half of an interval between the flow passages. The plate type heat exchanger is suitable for the oil cooler of a motorcar especially.